Review: Patch FORCE_NULL option for copy COPY in CSV mode

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
new file mode 100644
index 1ecc939..0038d03
*** a/doc/src/sgml/ref/copy.sgml
--- b/doc/src/sgml/ref/copy.sgml
*************** COPY { <replaceable class="parameter">ta
*** 42,47 ****
--- 42,48 ----
      ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
      FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
      FORCE_NOT_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
+     FORCE_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
      ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
  </synopsis>
   </refsynopsisdiv>
*************** COPY { <replaceable class="parameter">ta
*** 329,334 ****
--- 330,347 ----
     </varlistentry>

     <varlistentry>
+     <term><literal>FORCE_NULL</></term>
+     <listitem>
+      <para>
+       Force the specified columns' values to be converted to <literal>NULL</>
+       if the value contains an empty string.
+       This option is allowed only in <command>COPY FROM</>, and only when
+       using <literal>CSV</> format.
+      </para>
+     </listitem>
+    </varlistentry>
+
+    <varlistentry>
      <term><literal>ENCODING</></term>
      <listitem>
       <para>
*************** COPY <replaceable class="parameter">coun
*** 637,643 ****
      string, while an empty string data value is written with double quotes
      (<literal>""</>). Reading values follows similar rules. You can
      use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
!     comparisons for specific columns.
     </para>

     <para>
--- 650,658 ----
      string, while an empty string data value is written with double quotes
      (<literal>""</>). Reading values follows similar rules. You can
      use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
!     comparisons for specific columns. Alternatively you can use
!     <literal>FORCE_NULL</> to convert empty string data values to
!     <literal>NULL</>.
     </para>

     <para>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
new file mode 100644
index 6b20144..40a37a8
*** a/src/backend/commands/copy.c
--- b/src/backend/commands/copy.c
*************** typedef struct CopyStateData
*** 125,130 ****
--- 125,132 ----
  	bool	   *force_quote_flags;		/* per-column CSV FQ flags */
  	List	   *force_notnull;	/* list of column names */
  	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+ 	List	   *force_null;	/* list of column names */
+ 	bool	   *force_null_flags;	/* per-column CSV FN flags */
  	bool		convert_selectively;	/* do selective binary conversion? */
  	List	   *convert_select; /* list of column names (can be NIL) */
  	bool	   *convert_select_flags;	/* per-column CSV/TEXT CS flags */
*************** ProcessCopyOptions(CopyState cstate,
*** 1019,1024 ****
--- 1021,1040 ----
  						 errmsg("argument to option \"%s\" must be a list of column names",
  								defel->defname)));
  		}
+ 		else if (strcmp(defel->defname, "force_null") == 0)
+ 		{
+ 			if (cstate->force_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options")));
+ 			if (defel->arg && IsA(defel->arg, List))
+ 				cstate->force_null = (List *) defel->arg;
+ 			else
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ 						 errmsg("argument to option \"%s\" must be a list of column names",
+ 								defel->defname)));
+ 		}
  		else if (strcmp(defel->defname, "convert_selectively") == 0)
  		{
  			/*
*************** ProcessCopyOptions(CopyState cstate,
*** 1178,1183 ****
--- 1194,1210 ----
  				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
  			  errmsg("COPY force not null only available using COPY FROM")));

+ 	/* Check force_null */
+ 	if (!cstate->csv_mode && cstate->force_null != NIL)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ 				 errmsg("COPY force null available only in CSV mode")));
+
+ 	if (cstate->force_null != NIL && !is_from)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ 			  errmsg("COPY force null only available using COPY FROM")));
+
  	/* Don't allow the delimiter to appear in the null string. */
  	if (strchr(cstate->null_print, cstate->delim[0]) != NULL)
  		ereport(ERROR,
*************** BeginCopy(bool is_from,
*** 1385,1390 ****
--- 1412,1439 ----
  		}
  	}

+ 	/* Convert FORCE NULL name list to per-column flags, check validity */
+ 	cstate->force_null_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
+ 	if (cstate->force_null)
+ 	{
+ 		List	   *attnums;
+ 		ListCell   *cur;
+
+ 		attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->force_null);
+
+ 		foreach(cur, attnums)
+ 		{
+ 			int			attnum = lfirst_int(cur);
+
+ 			if (!list_member_int(cstate->attnumlist, attnum))
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+ 				errmsg("FORCE NULL column \"%s\" not referenced by COPY",
+ 					   NameStr(tupDesc->attrs[attnum - 1]->attname))));
+ 			cstate->force_null_flags[attnum - 1] = true;
+ 		}
+ 	}
+
  	/* Convert convert_selectively name list to per-column flags */
  	if (cstate->convert_selectively)
  	{
*************** NextCopyFrom(CopyState cstate, ExprConte
*** 2795,2805 ****
  				continue;
  			}

! 			if (cstate->csv_mode && string == NULL &&
! 				cstate->force_notnull_flags[m])
  			{
! 				/* Go ahead and read the NULL string */
! 				string = cstate->null_print;
  			}

  			cstate->cur_attname = NameStr(attr[m]->attname);
--- 2844,2867 ----
  				continue;
  			}

! 			if (cstate->csv_mode)
  			{
! 				if(string == NULL &&
! 				   cstate->force_notnull_flags[m])
! 				{
! 					/* FORCE_NOT_NULL option is set and column is NULL -
! 					   convert it to an empty string
! 					*/
! 					string = cstate->null_print;
! 				}
! 				else if(string != NULL && strlen(string) == 0 &&
! 						cstate->force_null_flags[m])
! 				{
! 					/* FORCE_NULL option is set and column is an empty string -
! 					   convert it to NULL
! 					*/
! 					string = NULL;
! 				}
  			}

  			cstate->cur_attname = NameStr(attr[m]->attname);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index a9812af..ca57ab7
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
*************** copy_opt_item:
*** 2493,2498 ****
--- 2493,2502 ----
  				{
  					$$ = makeDefElem("force_not_null", (Node *)$4);
  				}
+ 			| FORCE NULL_P columnList
+ 				{
+ 					$$ = makeDefElem("force_null", (Node *)$3);
+ 				}
  			| ENCODING Sconst
  				{
  					$$ = makeDefElem("encoding", (Node *)makeString($2));
diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
new file mode 100644
index 34fa131..de99108
*** a/src/test/regress/expected/copy2.out
--- b/src/test/regress/expected/copy2.out
*************** SELECT * FROM vistest;
*** 382,387 ****
--- 382,435 ----
   e
  (2 rows)

+ -- Test FORCE_NOT_NULL and FORCE_NULL options
+ -- should succeed with "b" set to an empty string and "c" set to NULL
+ CREATE TEMP TABLE forcetest (
+     a INT NOT NULL,
+     b TEXT NOT NULL,
+     c TEXT,
+     d TEXT,
+     e TEXT
+ );
+ \pset null NULL
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 1;
+  b |  c
+ ---+------
+    | NULL
+ (1 row)
+
+ -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 2;
+  b |  c
+ ---+------
+    | NULL
+ (1 row)
+
+ -- should fail with not-null constraint violiaton
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ ERROR:  null value in column "b" violates not-null constraint
+ DETAIL:  Failing row contains (3, null, , null, null).
+ CONTEXT:  COPY forcetest, line 1: "3,,"""
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ ERROR:  FORCE NOT NULL column "b" not referenced by COPY
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ ERROR:  FORCE NULL column "b" not referenced by COPY
+ ROLLBACK;
+ \pset null ''
+ DROP TABLE forcetest;
  DROP TABLE vistest;
  DROP FUNCTION truncate_in_subxact();
  DROP TABLE x, y;
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
new file mode 100644
index c46128b..b417cf7
*** a/src/test/regress/sql/copy2.sql
--- b/src/test/regress/sql/copy2.sql
*************** e
*** 270,275 ****
--- 270,314 ----
  SELECT * FROM vistest;
  COMMIT;
  SELECT * FROM vistest;
+ -- Test FORCE_NOT_NULL and FORCE_NULL options
+ -- should succeed with "b" set to an empty string and "c" set to NULL
+ CREATE TEMP TABLE forcetest (
+     a INT NOT NULL,
+     b TEXT NOT NULL,
+     c TEXT,
+     d TEXT,
+     e TEXT
+ );
+ \pset null NULL
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ 1,,""
+ \.
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 1;
+ -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ 2,,""
+ \.
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 2;
+ -- should fail with not-null constraint violiaton
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ 3,,""
+ \.
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ ROLLBACK;
+ \pset null ''
+ DROP TABLE forcetest;
  DROP TABLE vistest;
  DROP FUNCTION truncate_in_subxact();
  DROP TABLE x, y;

diff --git a/contrib/file_fdw/data/text.csv b/contrib/file_fdw/data/text.csv
new file mode 100644
index ed348a9..c7e243c
*** a/contrib/file_fdw/data/text.csv
--- b/contrib/file_fdw/data/text.csv
***************
*** 1,4 ****
! AAA,aaa
! XYZ,xyz
! NULL,NULL
! ABC,abc
--- 1,4 ----
! AAA,aaa,123,""
! XYZ,xyz,"",321
! NULL,NULL,NULL,NULL
! ABC,abc,"",""
diff --git a/contrib/file_fdw/file_fdw.c b/contrib/file_fdw/file_fdw.c
new file mode 100644
index 5639f4d..5877512
*** a/contrib/file_fdw/file_fdw.c
--- b/contrib/file_fdw/file_fdw.c
*************** struct FileFdwOption
*** 48,56 ****
  
  /*
   * Valid options for file_fdw.
!  * These options are based on the options for COPY FROM command.
!  * But note that force_not_null is handled as a boolean option attached to
!  * each column, not as a table option.
   *
   * Note: If you are adding new option for user mapping, you need to modify
   * fileGetOptions(), which currently doesn't bother to look at user mappings.
--- 48,56 ----
  
  /*
   * Valid options for file_fdw.
!  * These options are based on the options for the COPY FROM command.
!  * But note that force_not_null and force_null are handled as boolean options
!  * attached to a column, not as a table option.
   *
   * Note: If you are adding new option for user mapping, you need to modify
   * fileGetOptions(), which currently doesn't bother to look at user mappings.
*************** static const struct FileFdwOption valid_
*** 69,75 ****
  	{"null", ForeignTableRelationId},
  	{"encoding", ForeignTableRelationId},
  	{"force_not_null", AttributeRelationId},
! 
  	/*
  	 * force_quote is not supported by file_fdw because it's for COPY TO.
  	 */
--- 69,75 ----
  	{"null", ForeignTableRelationId},
  	{"encoding", ForeignTableRelationId},
  	{"force_not_null", AttributeRelationId},
! 	{"force_null", AttributeRelationId},
  	/*
  	 * force_quote is not supported by file_fdw because it's for COPY TO.
  	 */
*************** file_fdw_validator(PG_FUNCTION_ARGS)
*** 187,192 ****
--- 187,193 ----
  	Oid			catalog = PG_GETARG_OID(1);
  	char	   *filename = NULL;
  	DefElem    *force_not_null = NULL;
+ 	DefElem    *force_null = NULL;
  	List	   *other_options = NIL;
  	ListCell   *cell;
  
*************** file_fdw_validator(PG_FUNCTION_ARGS)
*** 243,252 ****
  		}
  
  		/*
! 		 * Separate out filename and force_not_null, since ProcessCopyOptions
! 		 * won't accept them.  (force_not_null only comes in a boolean
! 		 * per-column flavor here.)
  		 */
  		if (strcmp(def->defname, "filename") == 0)
  		{
  			if (filename)
--- 244,253 ----
  		}
  
  		/*
! 		 * Separate out filename and column-specific options, since
! 		 * ProcessCopyOptions won't accept them.
  		 */
+ 
  		if (strcmp(def->defname, "filename") == 0)
  		{
  			if (filename)
*************** file_fdw_validator(PG_FUNCTION_ARGS)
*** 255,270 ****
  						 errmsg("conflicting or redundant options")));
  			filename = defGetString(def);
  		}
  		else if (strcmp(def->defname, "force_not_null") == 0)
  		{
  			if (force_not_null)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
! 						 errmsg("conflicting or redundant options")));
  			force_not_null = def;
  			/* Don't care what the value is, as long as it's a legal boolean */
  			(void) defGetBoolean(def);
  		}
  		else
  			other_options = lappend(other_options, def);
  	}
--- 256,297 ----
  						 errmsg("conflicting or redundant options")));
  			filename = defGetString(def);
  		}
+ 		/*
+ 		 * force_not_null is a boolean option; after validation we can discard
+ 		 * it - it will be retrieved later in get_file_fdw_attribute_options()
+ 		 */
  		else if (strcmp(def->defname, "force_not_null") == 0)
  		{
  			if (force_not_null)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
! 						 errmsg("conflicting or redundant options"),
! 						 errhint("option \"force_not_null\" supplied more than once for a column")));
! 			if(force_null)
! 				ereport(ERROR,
! 						(errcode(ERRCODE_SYNTAX_ERROR),
! 						 errmsg("conflicting or redundant options"),
! 						 errhint("option \"force_not_null\" cannot be used together with \"force_null\"")));
  			force_not_null = def;
  			/* Don't care what the value is, as long as it's a legal boolean */
  			(void) defGetBoolean(def);
  		}
+ 		/* See comments for force_not_null above */
+ 		else if (strcmp(def->defname, "force_null") == 0)
+ 		{
+ 			if (force_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options"),
+ 						 errhint("option \"force_null\" supplied more than once for a column")));
+ 			if(force_not_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options"),
+ 						 errhint("option \"force_null\" cannot be used together with \"force_not_null\"")));
+ 			force_null = def;
+ 			(void) defGetBoolean(def);
+ 		}
  		else
  			other_options = lappend(other_options, def);
  	}
*************** fileGetOptions(Oid foreigntableid,
*** 369,375 ****
   * Retrieve per-column generic options from pg_attribute and construct a list
   * of DefElems representing them.
   *
!  * At the moment we only have "force_not_null", which should be combined into
   * a single DefElem listing all such columns, since that's what COPY expects.
   */
  static List *
--- 396,402 ----
   * Retrieve per-column generic options from pg_attribute and construct a list
   * of DefElems representing them.
   *
!  * At the moment we only have "force_not_null", which should be combined into XXX
   * a single DefElem listing all such columns, since that's what COPY expects.
   */
  static List *
*************** get_file_fdw_attribute_options(Oid relid
*** 380,385 ****
--- 407,415 ----
  	AttrNumber	natts;
  	AttrNumber	attnum;
  	List	   *fnncolumns = NIL;
+ 	List	   *fncolumns = NIL;
+ 
+ 	List *options = NIL;
  
  	rel = heap_open(relid, AccessShareLock);
  	tupleDesc = RelationGetDescr(rel);
*************** get_file_fdw_attribute_options(Oid relid
*** 410,426 ****
  					fnncolumns = lappend(fnncolumns, makeString(attname));
  				}
  			}
  			/* maybe in future handle other options here */
  		}
  	}
  
  	heap_close(rel, AccessShareLock);
  
! 	/* Return DefElem only when some column(s) have force_not_null */
  	if (fnncolumns != NIL)
! 		return list_make1(makeDefElem("force_not_null", (Node *) fnncolumns));
! 	else
! 		return NIL;
  }
  
  /*
--- 440,468 ----
  					fnncolumns = lappend(fnncolumns, makeString(attname));
  				}
  			}
+ 			else if (strcmp(def->defname, "force_null") == 0)
+ 			{
+ 				if (defGetBoolean(def))
+ 				{
+ 					char	   *attname = pstrdup(NameStr(attr->attname));
+ 
+ 					fncolumns = lappend(fncolumns, makeString(attname));
+ 				}
+ 			}
  			/* maybe in future handle other options here */
  		}
  	}
  
  	heap_close(rel, AccessShareLock);
  
! 	/* Return DefElem only when some column(s) have force_not_null / force_null options set */
  	if (fnncolumns != NIL)
! 		options = lappend(options, makeDefElem("force_not_null", (Node *) fnncolumns));
! 
! 	if (fncolumns != NIL)
! 		options = lappend(options,makeDefElem("force_null", (Node *) fncolumns));
! 
! 	return options;
  }
  
  /*
diff --git a/contrib/file_fdw/input/file_fdw.source b/contrib/file_fdw/input/file_fdw.source
new file mode 100644
index f7fd28d..0c278aa
*** a/contrib/file_fdw/input/file_fdw.source
--- b/contrib/file_fdw/input/file_fdw.source
*************** OPTIONS (format 'csv', filename '@abs_sr
*** 81,91 ****
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
  SELECT * FROM text_csv;
  
  -- force_not_null is not allowed to be specified at any foreign object level:
--- 81,94 ----
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off'),
!     word3 text OPTIONS (force_null 'true'),
!     word4 text OPTIONS (force_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
+ \pset null _null_
  SELECT * FROM text_csv;
  
  -- force_not_null is not allowed to be specified at any foreign object level:
*************** ALTER SERVER file_server OPTIONS (ADD fo
*** 94,99 ****
--- 97,114 ----
  CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
  CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
  
+ -- force_not_null cannot be specified together with force_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
+ 
+ -- force_null is not allowed to be specified at any foreign object level:
+ ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
+ ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
+ CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ 
+ -- force_null cannot be specified together with force_not_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
+ 
  -- basic query tests
  SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
  SELECT * FROM agg_csv ORDER BY a;
diff --git a/contrib/file_fdw/output/file_fdw.source b/contrib/file_fdw/output/file_fdw.source
new file mode 100644
index 4f90bae..aa6d164
*** a/contrib/file_fdw/output/file_fdw.source
--- b/contrib/file_fdw/output/file_fdw.source
*************** OPTIONS (format 'csv', filename '@abs_sr
*** 96,114 ****
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ERROR:  COPY force not null available only in CSV mode
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
  SELECT * FROM text_csv;
!  word1 | word2 
! -------+-------
!  AAA   | aaa
!  XYZ   | xyz
!  NULL  | 
!  ABC   | abc
  (4 rows)
  
  -- force_not_null is not allowed to be specified at any foreign object level:
--- 96,117 ----
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off'),
!     word3 text OPTIONS (force_null 'true'),
!     word4 text OPTIONS (force_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ERROR:  COPY force not null available only in CSV mode
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
+ \pset null _null_
  SELECT * FROM text_csv;
!  word1 | word2  | word3  | word4  
! -------+--------+--------+--------
!  AAA   | aaa    | 123    | 
!  XYZ   | xyz    | _null_ | 321
!  NULL  | _null_ | _null_ | _null_
!  ABC   | abc    | _null_ | 
  (4 rows)
  
  -- force_not_null is not allowed to be specified at any foreign object level:
*************** HINT:  There are no valid options in thi
*** 124,129 ****
--- 127,153 ----
  CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
  ERROR:  invalid option "force_not_null"
  HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
+ -- force_not_null cannot be specified together with force_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
+ ERROR:  conflicting or redundant options
+ HINT:  option "force_null" cannot be used together with "force_not_null"
+ -- force_null is not allowed to be specified at any foreign object level:
+ ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  There are no valid options in this context.
+ ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  There are no valid options in this context.
+ CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  There are no valid options in this context.
+ CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
+ -- force_null cannot be specified together with force_not_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
+ ERROR:  conflicting or redundant options
+ HINT:  option "force_not_null" cannot be used together with "force_null"
  -- basic query tests
  SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
    a  |   b    
diff --git a/doc/src/sgml/file-fdw.sgml b/doc/src/sgml/file-fdw.sgml
new file mode 100644
index 9385b26..88bfb36
*** a/doc/src/sgml/file-fdw.sgml
--- b/doc/src/sgml/file-fdw.sgml
***************
*** 112,122 ****
   </variablelist>
  
   <para>
!   Note that while <command>COPY</> allows options such as OIDS and HEADER 
    to be specified without a corresponding value, the foreign data wrapper
!   syntax requires a value to be present in all cases.  To activate 
    <command>COPY</> options normally supplied without a value, you can
!   instead pass the value TRUE. 
   </para>
  
   <para>
--- 112,122 ----
   </variablelist>
  
   <para>
!   Note that while <command>COPY</> allows options such as OIDS and HEADER
    to be specified without a corresponding value, the foreign data wrapper
!   syntax requires a value to be present in all cases.  To activate
    <command>COPY</> options normally supplied without a value, you can
!   instead pass the value TRUE.
   </para>
  
   <para>
***************
*** 139,144 ****
--- 139,157 ----
      </para>
     </listitem>
    </varlistentry>
+ 
+   <varlistentry>
+    <term><literal>force_null</literal></term>
+ 
+    <listitem>
+     <para>
+      This is a Boolean option.  If true, it specifies that values of the
+      column which would otherwise be treated as an empty string should be
+      inserted as a NULL. This has the same effect  as listing the column in
+      <command>COPY</>'s <literal>FORCE_NULL</literal> option.
+     </para>
+    </listitem>
+   </varlistentry>
  
   </variablelist>
  
diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
new file mode 100644
index 1ecc939..1888593
*** a/doc/src/sgml/ref/copy.sgml
--- b/doc/src/sgml/ref/copy.sgml
*************** COPY { <replaceable class="parameter">ta
*** 42,47 ****
--- 42,48 ----
      ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
      FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
      FORCE_NOT_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
+     FORCE_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
      ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
  </synopsis>
   </refsynopsisdiv>
*************** COPY { <replaceable class="parameter">ta
*** 329,334 ****
--- 330,347 ----
     </varlistentry>
  
     <varlistentry>
+     <term><literal>FORCE_NULL</></term>
+     <listitem>
+      <para>
+       Force the specified columns' values to be converted to <literal>NULL</>
+       if the value contains an empty string.
+       This option is allowed only in <command>COPY FROM</>, and only when
+       using <literal>CSV</> format.
+      </para>
+     </listitem>
+    </varlistentry>
+ 
+    <varlistentry>
      <term><literal>ENCODING</></term>
      <listitem>
       <para>
*************** COPY <replaceable class="parameter">coun
*** 637,643 ****
      string, while an empty string data value is written with double quotes
      (<literal>""</>). Reading values follows similar rules. You can
      use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
!     comparisons for specific columns.
     </para>
  
     <para>
--- 650,658 ----
      string, while an empty string data value is written with double quotes
      (<literal>""</>). Reading values follows similar rules. You can
      use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
!     comparisons for specific columns. Alternatively you can use
!     <literal>FORCE_NULL</> to convert empty string data values to
!     <literal>NULL</>.
     </para>
  
     <para>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
new file mode 100644
index 7c4039c..0f0d8c6
*** a/src/backend/commands/copy.c
--- b/src/backend/commands/copy.c
*************** typedef struct CopyStateData
*** 125,130 ****
--- 125,132 ----
  	bool	   *force_quote_flags;		/* per-column CSV FQ flags */
  	List	   *force_notnull;	/* list of column names */
  	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+ 	List	   *force_null;	/* list of column names */
+ 	bool	   *force_null_flags;	/* per-column CSV FN flags */
  	bool		convert_selectively;	/* do selective binary conversion? */
  	List	   *convert_select; /* list of column names (can be NIL) */
  	bool	   *convert_select_flags;	/* per-column CSV/TEXT CS flags */
*************** ProcessCopyOptions(CopyState cstate,
*** 1019,1024 ****
--- 1021,1040 ----
  						 errmsg("argument to option \"%s\" must be a list of column names",
  								defel->defname)));
  		}
+ 		else if (strcmp(defel->defname, "force_null") == 0)
+ 		{
+ 			if (cstate->force_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options")));
+ 			if (defel->arg && IsA(defel->arg, List))
+ 				cstate->force_null = (List *) defel->arg;
+ 			else
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ 						 errmsg("argument to option \"%s\" must be a list of column names",
+ 								defel->defname)));
+ 		}
  		else if (strcmp(defel->defname, "convert_selectively") == 0)
  		{
  			/*
*************** ProcessCopyOptions(CopyState cstate,
*** 1178,1183 ****
--- 1194,1210 ----
  				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
  			  errmsg("COPY force not null only available using COPY FROM")));
  
+ 	/* Check force_null */
+ 	if (!cstate->csv_mode && cstate->force_null != NIL)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ 				 errmsg("COPY force null available only in CSV mode")));
+ 
+ 	if (cstate->force_null != NIL && !is_from)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ 			  errmsg("COPY force null only available using COPY FROM")));
+ 
  	/* Don't allow the delimiter to appear in the null string. */
  	if (strchr(cstate->null_print, cstate->delim[0]) != NULL)
  		ereport(ERROR,
*************** BeginCopy(bool is_from,
*** 1385,1390 ****
--- 1412,1439 ----
  		}
  	}
  
+ 	/* Convert FORCE NULL name list to per-column flags, check validity */
+ 	cstate->force_null_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
+ 	if (cstate->force_null)
+ 	{
+ 		List	   *attnums;
+ 		ListCell   *cur;
+ 
+ 		attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->force_null);
+ 
+ 		foreach(cur, attnums)
+ 		{
+ 			int			attnum = lfirst_int(cur);
+ 
+ 			if (!list_member_int(cstate->attnumlist, attnum))
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+ 				errmsg("FORCE NULL column \"%s\" not referenced by COPY",
+ 					   NameStr(tupDesc->attrs[attnum - 1]->attname))));
+ 			cstate->force_null_flags[attnum - 1] = true;
+ 		}
+ 	}
+ 
  	/* Convert convert_selectively name list to per-column flags */
  	if (cstate->convert_selectively)
  	{
*************** NextCopyFrom(CopyState cstate, ExprConte
*** 2810,2820 ****
  				continue;
  			}
  
! 			if (cstate->csv_mode && string == NULL &&
! 				cstate->force_notnull_flags[m])
  			{
! 				/* Go ahead and read the NULL string */
! 				string = cstate->null_print;
  			}
  
  			cstate->cur_attname = NameStr(attr[m]->attname);
--- 2859,2882 ----
  				continue;
  			}
  
! 			if (cstate->csv_mode)
  			{
! 				if(string == NULL &&
! 				   cstate->force_notnull_flags[m])
! 				{
! 					/* FORCE_NOT_NULL option is set and column is NULL -
! 					   convert it to an empty string
! 					*/
! 					string = cstate->null_print;
! 				}
! 				else if(string != NULL && strlen(string) == 0 &&
! 						cstate->force_null_flags[m])
! 				{
! 					/* FORCE_NULL option is set and column is an empty string -
! 					   convert it to NULL
! 					*/
! 					string = NULL;
! 				}
  			}
  
  			cstate->cur_attname = NameStr(attr[m]->attname);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 0787eb7..7a1ff14
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
*************** copy_opt_item:
*** 2550,2555 ****
--- 2550,2559 ----
  				{
  					$$ = makeDefElem("force_not_null", (Node *)$4);
  				}
+ 			| FORCE NULL_P columnList
+ 				{
+ 					$$ = makeDefElem("force_null", (Node *)$3);
+ 				}
  			| ENCODING Sconst
  				{
  					$$ = makeDefElem("encoding", (Node *)makeString($2));
diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
new file mode 100644
index 34fa131..616bd9c
*** a/src/test/regress/expected/copy2.out
--- b/src/test/regress/expected/copy2.out
*************** SELECT * FROM vistest;
*** 382,387 ****
--- 382,435 ----
   e
  (2 rows)
  
+ -- Test FORCE_NOT_NULL and FORCE_NULL options
+ -- should succeed with "b" set to an empty string and "c" set to NULL
+ CREATE TEMP TABLE forcetest (
+     a INT NOT NULL,
+     b TEXT NOT NULL,
+     c TEXT,
+     d TEXT,
+     e TEXT
+ );
+ \pset null NULL
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 1;
+  b |  c
+ ---+------
+    | NULL
+ (1 row)
+ 
+ -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 2;
+  b |  c
+ ---+------
+    | NULL
+ (1 row)
+ 
+ -- should fail with not-null constraint violiaton
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ ERROR:  null value in column "b" violates not-null constraint
+ DETAIL:  Failing row contains (3, null, , null, null).
+ CONTEXT:  COPY forcetest, line 1: "3,,"""
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ ERROR:  FORCE NOT NULL column "b" not referenced by COPY
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ ERROR:  FORCE NULL column "b" not referenced by COPY
+ ROLLBACK;
+ \pset null ''
+ DROP TABLE forcetest;
  DROP TABLE vistest;
  DROP FUNCTION truncate_in_subxact();
  DROP TABLE x, y;
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
new file mode 100644
index c46128b..b417cf7
*** a/src/test/regress/sql/copy2.sql
--- b/src/test/regress/sql/copy2.sql
*************** e
*** 270,275 ****
--- 270,314 ----
  SELECT * FROM vistest;
  COMMIT;
  SELECT * FROM vistest;
+ -- Test FORCE_NOT_NULL and FORCE_NULL options
+ -- should succeed with "b" set to an empty string and "c" set to NULL
+ CREATE TEMP TABLE forcetest (
+     a INT NOT NULL,
+     b TEXT NOT NULL,
+     c TEXT,
+     d TEXT,
+     e TEXT
+ );
+ \pset null NULL
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ 1,,""
+ \.
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 1;
+ -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ 2,,""
+ \.
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 2;
+ -- should fail with not-null constraint violiaton
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ 3,,""
+ \.
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ ROLLBACK;
+ \pset null ''
+ DROP TABLE forcetest;
  DROP TABLE vistest;
  DROP FUNCTION truncate_in_subxact();
  DROP TABLE x, y;

diff --git a/contrib/file_fdw/data/text.csv b/contrib/file_fdw/data/text.csv
index ed348a9..f55d9cf 100644
--- a/contrib/file_fdw/data/text.csv
+++ b/contrib/file_fdw/data/text.csv
@@ -1,4 +1,5 @@
-AAA,aaa
-XYZ,xyz
-NULL,NULL
-ABC,abc
+AAA,aaa,123,""
+XYZ,xyz,"",321
+NULL,NULL,NULL,NULL
+NULL,NULL,"NULL",NULL
+ABC,abc,"",""
diff --git a/contrib/file_fdw/file_fdw.c b/contrib/file_fdw/file_fdw.c
index 5639f4d..7fb1dbc 100644
--- a/contrib/file_fdw/file_fdw.c
+++ b/contrib/file_fdw/file_fdw.c
@@ -48,9 +48,9 @@ struct FileFdwOption
 
 /*
  * Valid options for file_fdw.
- * These options are based on the options for COPY FROM command.
- * But note that force_not_null is handled as a boolean option attached to
- * each column, not as a table option.
+ * These options are based on the options for the COPY FROM command.
+ * But note that force_not_null and force_null are handled as boolean options
+ * attached to a column, not as table options.
  *
  * Note: If you are adding new option for user mapping, you need to modify
  * fileGetOptions(), which currently doesn't bother to look at user mappings.
@@ -69,7 +69,7 @@ static const struct FileFdwOption valid_options[] = {
 	{"null", ForeignTableRelationId},
 	{"encoding", ForeignTableRelationId},
 	{"force_not_null", AttributeRelationId},
-
+	{"force_null", AttributeRelationId},
 	/*
 	 * force_quote is not supported by file_fdw because it's for COPY TO.
 	 */
@@ -187,6 +187,7 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 	Oid			catalog = PG_GETARG_OID(1);
 	char	   *filename = NULL;
 	DefElem    *force_not_null = NULL;
+	DefElem    *force_null = NULL;
 	List	   *other_options = NIL;
 	ListCell   *cell;
 
@@ -243,10 +244,10 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 		}
 
 		/*
-		 * Separate out filename and force_not_null, since ProcessCopyOptions
-		 * won't accept them.  (force_not_null only comes in a boolean
-		 * per-column flavor here.)
+		 * Separate out filename and column-specific options, since
+		 * ProcessCopyOptions won't accept them.
 		 */
+
 		if (strcmp(def->defname, "filename") == 0)
 		{
 			if (filename)
@@ -255,16 +256,42 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 						 errmsg("conflicting or redundant options")));
 			filename = defGetString(def);
 		}
+		/*
+		 * force_not_null is a boolean option; after validation we can discard
+		 * it - it will be retrieved later in get_file_fdw_attribute_options()
+		 */
 		else if (strcmp(def->defname, "force_not_null") == 0)
 		{
 			if (force_not_null)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("conflicting or redundant options")));
+						 errmsg("conflicting or redundant options"),
+						 errhint("option \"force_not_null\" supplied more than once for a column")));
+			if(force_null)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 errhint("option \"force_not_null\" cannot be used together with \"force_null\"")));
 			force_not_null = def;
 			/* Don't care what the value is, as long as it's a legal boolean */
 			(void) defGetBoolean(def);
 		}
+		/* See comments for force_not_null above */
+		else if (strcmp(def->defname, "force_null") == 0)
+		{
+			if (force_null)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 errhint("option \"force_null\" supplied more than once for a column")));
+			if(force_not_null)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 errhint("option \"force_null\" cannot be used together with \"force_not_null\"")));
+			force_null = def;
+			(void) defGetBoolean(def);
+		}
 		else
 			other_options = lappend(other_options, def);
 	}
@@ -369,8 +396,9 @@ fileGetOptions(Oid foreigntableid,
  * Retrieve per-column generic options from pg_attribute and construct a list
  * of DefElems representing them.
  *
- * At the moment we only have "force_not_null", which should be combined into
- * a single DefElem listing all such columns, since that's what COPY expects.
+ * At the moment we only have "force_not_null", and "force_null",
+ * which should each be combined into a single DefElem listing all such
+ * columns, since that's what COPY expects.
  */
 static List *
 get_file_fdw_attribute_options(Oid relid)
@@ -380,6 +408,9 @@ get_file_fdw_attribute_options(Oid relid)
 	AttrNumber	natts;
 	AttrNumber	attnum;
 	List	   *fnncolumns = NIL;
+	List	   *fncolumns = NIL;
+
+	List *options = NIL;
 
 	rel = heap_open(relid, AccessShareLock);
 	tupleDesc = RelationGetDescr(rel);
@@ -410,17 +441,29 @@ get_file_fdw_attribute_options(Oid relid)
 					fnncolumns = lappend(fnncolumns, makeString(attname));
 				}
 			}
+			else if (strcmp(def->defname, "force_null") == 0)
+			{
+				if (defGetBoolean(def))
+				{
+					char	   *attname = pstrdup(NameStr(attr->attname));
+
+					fncolumns = lappend(fncolumns, makeString(attname));
+				}
+			}
 			/* maybe in future handle other options here */
 		}
 	}
 
 	heap_close(rel, AccessShareLock);
 
-	/* Return DefElem only when some column(s) have force_not_null */
+	/* Return DefElem only when some column(s) have force_not_null / force_null options set */
 	if (fnncolumns != NIL)
-		return list_make1(makeDefElem("force_not_null", (Node *) fnncolumns));
-	else
-		return NIL;
+		options = lappend(options, makeDefElem("force_not_null", (Node *) fnncolumns));
+
+	if (fncolumns != NIL)
+		options = lappend(options,makeDefElem("force_null", (Node *) fncolumns));
+
+	return options;
 }
 
 /*
diff --git a/contrib/file_fdw/input/file_fdw.source b/contrib/file_fdw/input/file_fdw.source
index f7fd28d..0c278aa 100644
--- a/contrib/file_fdw/input/file_fdw.source
+++ b/contrib/file_fdw/input/file_fdw.source
@@ -81,11 +81,14 @@ OPTIONS (format 'csv', filename '@abs_srcdir@/data/agg.bad', header 'true', deli
 -- per-column options tests
 CREATE FOREIGN TABLE text_csv (
     word1 text OPTIONS (force_not_null 'true'),
-    word2 text OPTIONS (force_not_null 'off')
+    word2 text OPTIONS (force_not_null 'off'),
+    word3 text OPTIONS (force_null 'true'),
+    word4 text OPTIONS (force_null 'off')
 ) SERVER file_server
 OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
 SELECT * FROM text_csv; -- ERROR
 ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
+\pset null _null_
 SELECT * FROM text_csv;
 
 -- force_not_null is not allowed to be specified at any foreign object level:
@@ -94,6 +97,18 @@ ALTER SERVER file_server OPTIONS (ADD force_not_null '*'); -- ERROR
 CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
 
+-- force_not_null cannot be specified together with force_null
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
+
+-- force_null is not allowed to be specified at any foreign object level:
+ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
+ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
+CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
+CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
+
+-- force_null cannot be specified together with force_not_null
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
+
 -- basic query tests
 SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
 SELECT * FROM agg_csv ORDER BY a;
diff --git a/contrib/file_fdw/output/file_fdw.source b/contrib/file_fdw/output/file_fdw.source
index 4f90bae..aa6d164 100644
--- a/contrib/file_fdw/output/file_fdw.source
+++ b/contrib/file_fdw/output/file_fdw.source
@@ -96,19 +96,22 @@ OPTIONS (format 'csv', filename '@abs_srcdir@/data/agg.bad', header 'true', deli
 -- per-column options tests
 CREATE FOREIGN TABLE text_csv (
     word1 text OPTIONS (force_not_null 'true'),
-    word2 text OPTIONS (force_not_null 'off')
+    word2 text OPTIONS (force_not_null 'off'),
+    word3 text OPTIONS (force_null 'true'),
+    word4 text OPTIONS (force_null 'off')
 ) SERVER file_server
 OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
 SELECT * FROM text_csv; -- ERROR
 ERROR:  COPY force not null available only in CSV mode
 ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
+\pset null _null_
 SELECT * FROM text_csv;
- word1 | word2 
--------+-------
- AAA   | aaa
- XYZ   | xyz
- NULL  | 
- ABC   | abc
+ word1 | word2  | word3  | word4  
+-------+--------+--------+--------
+ AAA   | aaa    | 123    | 
+ XYZ   | xyz    | _null_ | 321
+ NULL  | _null_ | _null_ | _null_
+ ABC   | abc    | _null_ | 
 (4 rows)
 
 -- force_not_null is not allowed to be specified at any foreign object level:
@@ -124,6 +127,27 @@ HINT:  There are no valid options in this context.
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
 ERROR:  invalid option "force_not_null"
 HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
+-- force_not_null cannot be specified together with force_null
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
+ERROR:  conflicting or redundant options
+HINT:  option "force_null" cannot be used together with "force_not_null"
+-- force_null is not allowed to be specified at any foreign object level:
+ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
+ERROR:  invalid option "force_null"
+HINT:  There are no valid options in this context.
+ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
+ERROR:  invalid option "force_null"
+HINT:  There are no valid options in this context.
+CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ERROR:  invalid option "force_null"
+HINT:  There are no valid options in this context.
+CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ERROR:  invalid option "force_null"
+HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
+-- force_null cannot be specified together with force_not_null
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
+ERROR:  conflicting or redundant options
+HINT:  option "force_not_null" cannot be used together with "force_null"
 -- basic query tests
 SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
   a  |   b    
diff --git a/doc/src/sgml/file-fdw.sgml b/doc/src/sgml/file-fdw.sgml
index 9385b26..d3b39aa 100644
--- a/doc/src/sgml/file-fdw.sgml
+++ b/doc/src/sgml/file-fdw.sgml
@@ -112,11 +112,11 @@
  </variablelist>
 
  <para>
-  Note that while <command>COPY</> allows options such as OIDS and HEADER 
+  Note that while <command>COPY</> allows options such as OIDS and HEADER
   to be specified without a corresponding value, the foreign data wrapper
-  syntax requires a value to be present in all cases.  To activate 
+  syntax requires a value to be present in all cases.  To activate
   <command>COPY</> options normally supplied without a value, you can
-  instead pass the value TRUE. 
+  instead pass the value TRUE.
  </para>
 
  <para>
@@ -140,6 +140,21 @@
    </listitem>
   </varlistentry>
 
+  <varlistentry>
+   <term><literal>force_null</literal></term>
+
+   <listitem>
+    <para>
+     This is a Boolean option.  If true, it specifies that values of the
+     column which match the null string are returned as <literal>NULL</>
+     even if the value is quoted. Without this option, only unquoted
+     values matching the null string are returned as <literal>NULL</>.
+     This has the same effect  as listing the column in
+     <command>COPY</>'s <literal>FORCE_NULL</literal> option.
+    </para>
+   </listitem>
+  </varlistentry>
+
  </variablelist>
 
  <para>
diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 99f246a..5be3514 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -42,6 +42,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
     FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NOT_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
+    FORCE_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
     ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
 </synopsis>
  </refsynopsisdiv>
@@ -329,6 +330,20 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
    </varlistentry>
 
    <varlistentry>
+    <term><literal>FORCE_NULL</></term>
+    <listitem>
+     <para>
+      Match the specified columns' values against the null string, even
+      if it has been quoted, and if a match is found set the value to
+      <literal>NULL</>. In the default case where the null string is empty,
+      this converts a quoted empty string into NULL.
+      This option is allowed only in <command>COPY FROM</>, and only when
+      using <literal>CSV</> format.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>ENCODING</></term>
     <listitem>
      <para>
@@ -637,7 +652,9 @@ COPY <replaceable class="parameter">count</replaceable>
     string, while an empty string data value is written with double quotes
     (<literal>""</>). Reading values follows similar rules. You can
     use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
-    comparisons for specific columns.
+    comparisons for specific columns. You can also use
+    <literal>FORCE_NULL</> to convert quoted null string data values to
+    <literal>NULL</>.
    </para>
 
    <para>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 7c4039c..70ee7e5 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -125,6 +125,8 @@ typedef struct CopyStateData
 	bool	   *force_quote_flags;		/* per-column CSV FQ flags */
 	List	   *force_notnull;	/* list of column names */
 	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+	List	   *force_null;	/* list of column names */
+	bool	   *force_null_flags;	/* per-column CSV FN flags */
 	bool		convert_selectively;	/* do selective binary conversion? */
 	List	   *convert_select; /* list of column names (can be NIL) */
 	bool	   *convert_select_flags;	/* per-column CSV/TEXT CS flags */
@@ -1019,6 +1021,20 @@ ProcessCopyOptions(CopyState cstate,
 						 errmsg("argument to option \"%s\" must be a list of column names",
 								defel->defname)));
 		}
+		else if (strcmp(defel->defname, "force_null") == 0)
+		{
+			if (cstate->force_null)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			if (defel->arg && IsA(defel->arg, List))
+				cstate->force_null = (List *) defel->arg;
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("argument to option \"%s\" must be a list of column names",
+								defel->defname)));
+		}
 		else if (strcmp(defel->defname, "convert_selectively") == 0)
 		{
 			/*
@@ -1178,6 +1194,17 @@ ProcessCopyOptions(CopyState cstate,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 			  errmsg("COPY force not null only available using COPY FROM")));
 
+	/* Check force_null */
+	if (!cstate->csv_mode && cstate->force_null != NIL)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("COPY force null available only in CSV mode")));
+
+	if (cstate->force_null != NIL && !is_from)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			  errmsg("COPY force null only available using COPY FROM")));
+
 	/* Don't allow the delimiter to appear in the null string. */
 	if (strchr(cstate->null_print, cstate->delim[0]) != NULL)
 		ereport(ERROR,
@@ -1385,6 +1412,28 @@ BeginCopy(bool is_from,
 		}
 	}
 
+	/* Convert FORCE NULL name list to per-column flags, check validity */
+	cstate->force_null_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
+	if (cstate->force_null)
+	{
+		List	   *attnums;
+		ListCell   *cur;
+
+		attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->force_null);
+
+		foreach(cur, attnums)
+		{
+			int			attnum = lfirst_int(cur);
+
+			if (!list_member_int(cstate->attnumlist, attnum))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+				errmsg("FORCE NULL column \"%s\" not referenced by COPY",
+					   NameStr(tupDesc->attrs[attnum - 1]->attname))));
+			cstate->force_null_flags[attnum - 1] = true;
+		}
+	}
+
 	/* Convert convert_selectively name list to per-column flags */
 	if (cstate->convert_selectively)
 	{
@@ -2810,11 +2859,28 @@ NextCopyFrom(CopyState cstate, ExprContext *econtext,
 				continue;
 			}
 
-			if (cstate->csv_mode && string == NULL &&
-				cstate->force_notnull_flags[m])
+			if (cstate->csv_mode)
 			{
-				/* Go ahead and read the NULL string */
-				string = cstate->null_print;
+				if(string == NULL &&
+				   cstate->force_notnull_flags[m])
+				{
+					/*
+					 * FORCE_NOT_NULL option is set and column is NULL -
+					 * convert it to the NULL string.
+					 */
+					string = cstate->null_print;
+				}
+				else if(string != NULL && cstate->force_null_flags[m]
+						&& strcmp(string,cstate->null_print) == 0 )
+				{
+					/*
+					 * FORCE_NULL option is set and column matches the NULL string.
+					 * It must have been quoted, or otherwise the string would already
+					 * have been set to NULL.
+					 * Convert it to NULL as specified.
+					 */
+					string = NULL;
+				}
 			}
 
 			cstate->cur_attname = NameStr(attr[m]->attname);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 81169a4..e3060a4 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -2548,6 +2548,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("force_not_null", (Node *)$4);
 				}
+			| FORCE NULL_P columnList
+				{
+					$$ = makeDefElem("force_null", (Node *)$3);
+				}
 			| ENCODING Sconst
 				{
 					$$ = makeDefElem("encoding", (Node *)makeString($2));
diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
index 34fa131..de99108 100644
--- a/src/test/regress/expected/copy2.out
+++ b/src/test/regress/expected/copy2.out
@@ -382,6 +382,54 @@ SELECT * FROM vistest;
  e
 (2 rows)
 
+-- Test FORCE_NOT_NULL and FORCE_NULL options
+-- should succeed with "b" set to an empty string and "c" set to NULL
+CREATE TEMP TABLE forcetest (
+    a INT NOT NULL,
+    b TEXT NOT NULL,
+    c TEXT,
+    d TEXT,
+    e TEXT
+);
+\pset null NULL
+BEGIN;
+COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+COMMIT;
+SELECT b, c FROM forcetest WHERE a = 1;
+ b |  c   
+---+------
+   | NULL
+(1 row)
+
+-- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+BEGIN;
+COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+COMMIT;
+SELECT b, c FROM forcetest WHERE a = 2;
+ b |  c   
+---+------
+   | NULL
+(1 row)
+
+-- should fail with not-null constraint violiaton
+BEGIN;
+COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ERROR:  null value in column "b" violates not-null constraint
+DETAIL:  Failing row contains (3, null, , null, null).
+CONTEXT:  COPY forcetest, line 1: "3,,"""
+ROLLBACK;
+-- should fail with "not referenced by COPY" error
+BEGIN;
+COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ERROR:  FORCE NOT NULL column "b" not referenced by COPY
+ROLLBACK;
+-- should fail with "not referenced by COPY" error
+BEGIN;
+COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ERROR:  FORCE NULL column "b" not referenced by COPY
+ROLLBACK;
+\pset null ''
+DROP TABLE forcetest;
 DROP TABLE vistest;
 DROP FUNCTION truncate_in_subxact();
 DROP TABLE x, y;
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
index c46128b..b417cf7 100644
--- a/src/test/regress/sql/copy2.sql
+++ b/src/test/regress/sql/copy2.sql
@@ -270,6 +270,45 @@ e
 SELECT * FROM vistest;
 COMMIT;
 SELECT * FROM vistest;
+-- Test FORCE_NOT_NULL and FORCE_NULL options
+-- should succeed with "b" set to an empty string and "c" set to NULL
+CREATE TEMP TABLE forcetest (
+    a INT NOT NULL,
+    b TEXT NOT NULL,
+    c TEXT,
+    d TEXT,
+    e TEXT
+);
+\pset null NULL
+BEGIN;
+COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+1,,""
+\.
+COMMIT;
+SELECT b, c FROM forcetest WHERE a = 1;
+-- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+BEGIN;
+COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+2,,""
+\.
+COMMIT;
+SELECT b, c FROM forcetest WHERE a = 2;
+-- should fail with not-null constraint violiaton
+BEGIN;
+COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+3,,""
+\.
+ROLLBACK;
+-- should fail with "not referenced by COPY" error
+BEGIN;
+COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ROLLBACK;
+-- should fail with "not referenced by COPY" error
+BEGIN;
+COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ROLLBACK;
+\pset null ''
+DROP TABLE forcetest;
 DROP TABLE vistest;
 DROP FUNCTION truncate_in_subxact();
 DROP TABLE x, y;

diff --git a/contrib/file_fdw/data/text.csv b/contrib/file_fdw/data/text.csv
new file mode 100644
index ed348a9..f55d9cf
*** a/contrib/file_fdw/data/text.csv
--- b/contrib/file_fdw/data/text.csv
***************
*** 1,4 ****
! AAA,aaa
! XYZ,xyz
! NULL,NULL
! ABC,abc
--- 1,5 ----
! AAA,aaa,123,""
! XYZ,xyz,"",321
! NULL,NULL,NULL,NULL
! NULL,NULL,"NULL",NULL
! ABC,abc,"",""
diff --git a/contrib/file_fdw/file_fdw.c b/contrib/file_fdw/file_fdw.c
new file mode 100644
index 5639f4d..7fb1dbc
*** a/contrib/file_fdw/file_fdw.c
--- b/contrib/file_fdw/file_fdw.c
*************** struct FileFdwOption
*** 48,56 ****
  
  /*
   * Valid options for file_fdw.
!  * These options are based on the options for COPY FROM command.
!  * But note that force_not_null is handled as a boolean option attached to
!  * each column, not as a table option.
   *
   * Note: If you are adding new option for user mapping, you need to modify
   * fileGetOptions(), which currently doesn't bother to look at user mappings.
--- 48,56 ----
  
  /*
   * Valid options for file_fdw.
!  * These options are based on the options for the COPY FROM command.
!  * But note that force_not_null and force_null are handled as boolean options
!  * attached to a column, not as table options.
   *
   * Note: If you are adding new option for user mapping, you need to modify
   * fileGetOptions(), which currently doesn't bother to look at user mappings.
*************** static const struct FileFdwOption valid_
*** 69,75 ****
  	{"null", ForeignTableRelationId},
  	{"encoding", ForeignTableRelationId},
  	{"force_not_null", AttributeRelationId},
! 
  	/*
  	 * force_quote is not supported by file_fdw because it's for COPY TO.
  	 */
--- 69,75 ----
  	{"null", ForeignTableRelationId},
  	{"encoding", ForeignTableRelationId},
  	{"force_not_null", AttributeRelationId},
! 	{"force_null", AttributeRelationId},
  	/*
  	 * force_quote is not supported by file_fdw because it's for COPY TO.
  	 */
*************** file_fdw_validator(PG_FUNCTION_ARGS)
*** 187,192 ****
--- 187,193 ----
  	Oid			catalog = PG_GETARG_OID(1);
  	char	   *filename = NULL;
  	DefElem    *force_not_null = NULL;
+ 	DefElem    *force_null = NULL;
  	List	   *other_options = NIL;
  	ListCell   *cell;
  
*************** file_fdw_validator(PG_FUNCTION_ARGS)
*** 243,252 ****
  		}
  
  		/*
! 		 * Separate out filename and force_not_null, since ProcessCopyOptions
! 		 * won't accept them.  (force_not_null only comes in a boolean
! 		 * per-column flavor here.)
  		 */
  		if (strcmp(def->defname, "filename") == 0)
  		{
  			if (filename)
--- 244,253 ----
  		}
  
  		/*
! 		 * Separate out filename and column-specific options, since
! 		 * ProcessCopyOptions won't accept them.
  		 */
+ 
  		if (strcmp(def->defname, "filename") == 0)
  		{
  			if (filename)
*************** file_fdw_validator(PG_FUNCTION_ARGS)
*** 255,270 ****
  						 errmsg("conflicting or redundant options")));
  			filename = defGetString(def);
  		}
  		else if (strcmp(def->defname, "force_not_null") == 0)
  		{
  			if (force_not_null)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
! 						 errmsg("conflicting or redundant options")));
  			force_not_null = def;
  			/* Don't care what the value is, as long as it's a legal boolean */
  			(void) defGetBoolean(def);
  		}
  		else
  			other_options = lappend(other_options, def);
  	}
--- 256,297 ----
  						 errmsg("conflicting or redundant options")));
  			filename = defGetString(def);
  		}
+ 		/*
+ 		 * force_not_null is a boolean option; after validation we can discard
+ 		 * it - it will be retrieved later in get_file_fdw_attribute_options()
+ 		 */
  		else if (strcmp(def->defname, "force_not_null") == 0)
  		{
  			if (force_not_null)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
! 						 errmsg("conflicting or redundant options"),
! 						 errhint("option \"force_not_null\" supplied more than once for a column")));
! 			if(force_null)
! 				ereport(ERROR,
! 						(errcode(ERRCODE_SYNTAX_ERROR),
! 						 errmsg("conflicting or redundant options"),
! 						 errhint("option \"force_not_null\" cannot be used together with \"force_null\"")));
  			force_not_null = def;
  			/* Don't care what the value is, as long as it's a legal boolean */
  			(void) defGetBoolean(def);
  		}
+ 		/* See comments for force_not_null above */
+ 		else if (strcmp(def->defname, "force_null") == 0)
+ 		{
+ 			if (force_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options"),
+ 						 errhint("option \"force_null\" supplied more than once for a column")));
+ 			if(force_not_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options"),
+ 						 errhint("option \"force_null\" cannot be used together with \"force_not_null\"")));
+ 			force_null = def;
+ 			(void) defGetBoolean(def);
+ 		}
  		else
  			other_options = lappend(other_options, def);
  	}
*************** fileGetOptions(Oid foreigntableid,
*** 369,376 ****
   * Retrieve per-column generic options from pg_attribute and construct a list
   * of DefElems representing them.
   *
!  * At the moment we only have "force_not_null", which should be combined into
!  * a single DefElem listing all such columns, since that's what COPY expects.
   */
  static List *
  get_file_fdw_attribute_options(Oid relid)
--- 396,404 ----
   * Retrieve per-column generic options from pg_attribute and construct a list
   * of DefElems representing them.
   *
!  * At the moment we only have "force_not_null", and "force_null",
!  * which should each be combined into a single DefElem listing all such
!  * columns, since that's what COPY expects.
   */
  static List *
  get_file_fdw_attribute_options(Oid relid)
*************** get_file_fdw_attribute_options(Oid relid
*** 380,385 ****
--- 408,416 ----
  	AttrNumber	natts;
  	AttrNumber	attnum;
  	List	   *fnncolumns = NIL;
+ 	List	   *fncolumns = NIL;
+ 
+ 	List *options = NIL;
  
  	rel = heap_open(relid, AccessShareLock);
  	tupleDesc = RelationGetDescr(rel);
*************** get_file_fdw_attribute_options(Oid relid
*** 410,426 ****
  					fnncolumns = lappend(fnncolumns, makeString(attname));
  				}
  			}
  			/* maybe in future handle other options here */
  		}
  	}
  
  	heap_close(rel, AccessShareLock);
  
! 	/* Return DefElem only when some column(s) have force_not_null */
  	if (fnncolumns != NIL)
! 		return list_make1(makeDefElem("force_not_null", (Node *) fnncolumns));
! 	else
! 		return NIL;
  }
  
  /*
--- 441,469 ----
  					fnncolumns = lappend(fnncolumns, makeString(attname));
  				}
  			}
+ 			else if (strcmp(def->defname, "force_null") == 0)
+ 			{
+ 				if (defGetBoolean(def))
+ 				{
+ 					char	   *attname = pstrdup(NameStr(attr->attname));
+ 
+ 					fncolumns = lappend(fncolumns, makeString(attname));
+ 				}
+ 			}
  			/* maybe in future handle other options here */
  		}
  	}
  
  	heap_close(rel, AccessShareLock);
  
! 	/* Return DefElem only when some column(s) have force_not_null / force_null options set */
  	if (fnncolumns != NIL)
! 		options = lappend(options, makeDefElem("force_not_null", (Node *) fnncolumns));
! 
! 	if (fncolumns != NIL)
! 		options = lappend(options,makeDefElem("force_null", (Node *) fncolumns));
! 
! 	return options;
  }
  
  /*
diff --git a/contrib/file_fdw/input/file_fdw.source b/contrib/file_fdw/input/file_fdw.source
new file mode 100644
index f7fd28d..0c278aa
*** a/contrib/file_fdw/input/file_fdw.source
--- b/contrib/file_fdw/input/file_fdw.source
*************** OPTIONS (format 'csv', filename '@abs_sr
*** 81,91 ****
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
  SELECT * FROM text_csv;
  
  -- force_not_null is not allowed to be specified at any foreign object level:
--- 81,94 ----
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off'),
!     word3 text OPTIONS (force_null 'true'),
!     word4 text OPTIONS (force_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
+ \pset null _null_
  SELECT * FROM text_csv;
  
  -- force_not_null is not allowed to be specified at any foreign object level:
*************** ALTER SERVER file_server OPTIONS (ADD fo
*** 94,99 ****
--- 97,114 ----
  CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
  CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
  
+ -- force_not_null cannot be specified together with force_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
+ 
+ -- force_null is not allowed to be specified at any foreign object level:
+ ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
+ ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
+ CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ 
+ -- force_null cannot be specified together with force_not_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
+ 
  -- basic query tests
  SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
  SELECT * FROM agg_csv ORDER BY a;
diff --git a/contrib/file_fdw/output/file_fdw.source b/contrib/file_fdw/output/file_fdw.source
new file mode 100644
index 4f90bae..2bec160
*** a/contrib/file_fdw/output/file_fdw.source
--- b/contrib/file_fdw/output/file_fdw.source
*************** OPTIONS (format 'csv', filename '@abs_sr
*** 96,115 ****
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ERROR:  COPY force not null available only in CSV mode
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
  SELECT * FROM text_csv;
!  word1 | word2 
! -------+-------
!  AAA   | aaa
!  XYZ   | xyz
!  NULL  | 
!  ABC   | abc
! (4 rows)
  
  -- force_not_null is not allowed to be specified at any foreign object level:
  ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_not_null '*'); -- ERROR
--- 96,119 ----
  -- per-column options tests
  CREATE FOREIGN TABLE text_csv (
      word1 text OPTIONS (force_not_null 'true'),
!     word2 text OPTIONS (force_not_null 'off'),
!     word3 text OPTIONS (force_null 'true'),
!     word4 text OPTIONS (force_null 'off')
  ) SERVER file_server
  OPTIONS (format 'text', filename '@abs_srcdir@/data/text.csv', null 'NULL');
  SELECT * FROM text_csv; -- ERROR
  ERROR:  COPY force not null available only in CSV mode
  ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
+ \pset null _null_
  SELECT * FROM text_csv;
!  word1 | word2  | word3  | word4  
! -------+--------+--------+--------
!  AAA   | aaa    | 123    | 
!  XYZ   | xyz    |        | 321
!  NULL  | _null_ | _null_ | _null_
!  NULL  | _null_ | _null_ | _null_
!  ABC   | abc    |        | 
! (5 rows)
  
  -- force_not_null is not allowed to be specified at any foreign object level:
  ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_not_null '*'); -- ERROR
*************** HINT:  There are no valid options in thi
*** 124,129 ****
--- 128,154 ----
  CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
  ERROR:  invalid option "force_not_null"
  HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
+ -- force_not_null cannot be specified together with force_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
+ ERROR:  conflicting or redundant options
+ HINT:  option "force_null" cannot be used together with "force_not_null"
+ -- force_null is not allowed to be specified at any foreign object level:
+ ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  There are no valid options in this context.
+ ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  There are no valid options in this context.
+ CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  There are no valid options in this context.
+ CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
+ ERROR:  invalid option "force_null"
+ HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
+ -- force_null cannot be specified together with force_not_null
+ ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
+ ERROR:  conflicting or redundant options
+ HINT:  option "force_not_null" cannot be used together with "force_null"
  -- basic query tests
  SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
    a  |   b    
diff --git a/doc/src/sgml/file-fdw.sgml b/doc/src/sgml/file-fdw.sgml
new file mode 100644
index 9385b26..d3b39aa
*** a/doc/src/sgml/file-fdw.sgml
--- b/doc/src/sgml/file-fdw.sgml
***************
*** 112,122 ****
   </variablelist>
  
   <para>
!   Note that while <command>COPY</> allows options such as OIDS and HEADER 
    to be specified without a corresponding value, the foreign data wrapper
!   syntax requires a value to be present in all cases.  To activate 
    <command>COPY</> options normally supplied without a value, you can
!   instead pass the value TRUE. 
   </para>
  
   <para>
--- 112,122 ----
   </variablelist>
  
   <para>
!   Note that while <command>COPY</> allows options such as OIDS and HEADER
    to be specified without a corresponding value, the foreign data wrapper
!   syntax requires a value to be present in all cases.  To activate
    <command>COPY</> options normally supplied without a value, you can
!   instead pass the value TRUE.
   </para>
  
   <para>
***************
*** 139,144 ****
--- 139,159 ----
      </para>
     </listitem>
    </varlistentry>
+ 
+   <varlistentry>
+    <term><literal>force_null</literal></term>
+ 
+    <listitem>
+     <para>
+      This is a Boolean option.  If true, it specifies that values of the
+      column which match the null string are returned as <literal>NULL</>
+      even if the value is quoted. Without this option, only unquoted
+      values matching the null string are returned as <literal>NULL</>.
+      This has the same effect  as listing the column in
+      <command>COPY</>'s <literal>FORCE_NULL</literal> option.
+     </para>
+    </listitem>
+   </varlistentry>
  
   </variablelist>
  
diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
new file mode 100644
index 99f246a..5be3514
*** a/doc/src/sgml/ref/copy.sgml
--- b/doc/src/sgml/ref/copy.sgml
*************** COPY { <replaceable class="parameter">ta
*** 42,47 ****
--- 42,48 ----
      ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
      FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
      FORCE_NOT_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
+     FORCE_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
      ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
  </synopsis>
   </refsynopsisdiv>
*************** COPY { <replaceable class="parameter">ta
*** 329,334 ****
--- 330,349 ----
     </varlistentry>
  
     <varlistentry>
+     <term><literal>FORCE_NULL</></term>
+     <listitem>
+      <para>
+       Match the specified columns' values against the null string, even
+       if it has been quoted, and if a match is found set the value to
+       <literal>NULL</>. In the default case where the null string is empty,
+       this converts a quoted empty string into NULL.
+       This option is allowed only in <command>COPY FROM</>, and only when
+       using <literal>CSV</> format.
+      </para>
+     </listitem>
+    </varlistentry>
+ 
+    <varlistentry>
      <term><literal>ENCODING</></term>
      <listitem>
       <para>
*************** COPY <replaceable class="parameter">coun
*** 637,643 ****
      string, while an empty string data value is written with double quotes
      (<literal>""</>). Reading values follows similar rules. You can
      use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
!     comparisons for specific columns.
     </para>
  
     <para>
--- 652,660 ----
      string, while an empty string data value is written with double quotes
      (<literal>""</>). Reading values follows similar rules. You can
      use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
!     comparisons for specific columns. You can also use
!     <literal>FORCE_NULL</> to convert quoted null string data values to
!     <literal>NULL</>.
     </para>
  
     <para>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
new file mode 100644
index 7c4039c..70ee7e5
*** a/src/backend/commands/copy.c
--- b/src/backend/commands/copy.c
*************** typedef struct CopyStateData
*** 125,130 ****
--- 125,132 ----
  	bool	   *force_quote_flags;		/* per-column CSV FQ flags */
  	List	   *force_notnull;	/* list of column names */
  	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+ 	List	   *force_null;	/* list of column names */
+ 	bool	   *force_null_flags;	/* per-column CSV FN flags */
  	bool		convert_selectively;	/* do selective binary conversion? */
  	List	   *convert_select; /* list of column names (can be NIL) */
  	bool	   *convert_select_flags;	/* per-column CSV/TEXT CS flags */
*************** ProcessCopyOptions(CopyState cstate,
*** 1019,1024 ****
--- 1021,1040 ----
  						 errmsg("argument to option \"%s\" must be a list of column names",
  								defel->defname)));
  		}
+ 		else if (strcmp(defel->defname, "force_null") == 0)
+ 		{
+ 			if (cstate->force_null)
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_SYNTAX_ERROR),
+ 						 errmsg("conflicting or redundant options")));
+ 			if (defel->arg && IsA(defel->arg, List))
+ 				cstate->force_null = (List *) defel->arg;
+ 			else
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ 						 errmsg("argument to option \"%s\" must be a list of column names",
+ 								defel->defname)));
+ 		}
  		else if (strcmp(defel->defname, "convert_selectively") == 0)
  		{
  			/*
*************** ProcessCopyOptions(CopyState cstate,
*** 1178,1183 ****
--- 1194,1210 ----
  				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
  			  errmsg("COPY force not null only available using COPY FROM")));
  
+ 	/* Check force_null */
+ 	if (!cstate->csv_mode && cstate->force_null != NIL)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ 				 errmsg("COPY force null available only in CSV mode")));
+ 
+ 	if (cstate->force_null != NIL && !is_from)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ 			  errmsg("COPY force null only available using COPY FROM")));
+ 
  	/* Don't allow the delimiter to appear in the null string. */
  	if (strchr(cstate->null_print, cstate->delim[0]) != NULL)
  		ereport(ERROR,
*************** BeginCopy(bool is_from,
*** 1385,1390 ****
--- 1412,1439 ----
  		}
  	}
  
+ 	/* Convert FORCE NULL name list to per-column flags, check validity */
+ 	cstate->force_null_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
+ 	if (cstate->force_null)
+ 	{
+ 		List	   *attnums;
+ 		ListCell   *cur;
+ 
+ 		attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->force_null);
+ 
+ 		foreach(cur, attnums)
+ 		{
+ 			int			attnum = lfirst_int(cur);
+ 
+ 			if (!list_member_int(cstate->attnumlist, attnum))
+ 				ereport(ERROR,
+ 						(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+ 				errmsg("FORCE NULL column \"%s\" not referenced by COPY",
+ 					   NameStr(tupDesc->attrs[attnum - 1]->attname))));
+ 			cstate->force_null_flags[attnum - 1] = true;
+ 		}
+ 	}
+ 
  	/* Convert convert_selectively name list to per-column flags */
  	if (cstate->convert_selectively)
  	{
*************** NextCopyFrom(CopyState cstate, ExprConte
*** 2810,2820 ****
  				continue;
  			}
  
! 			if (cstate->csv_mode && string == NULL &&
! 				cstate->force_notnull_flags[m])
  			{
! 				/* Go ahead and read the NULL string */
! 				string = cstate->null_print;
  			}
  
  			cstate->cur_attname = NameStr(attr[m]->attname);
--- 2859,2886 ----
  				continue;
  			}
  
! 			if (cstate->csv_mode)
  			{
! 				if(string == NULL &&
! 				   cstate->force_notnull_flags[m])
! 				{
! 					/*
! 					 * FORCE_NOT_NULL option is set and column is NULL -
! 					 * convert it to the NULL string.
! 					 */
! 					string = cstate->null_print;
! 				}
! 				else if(string != NULL && cstate->force_null_flags[m]
! 						&& strcmp(string,cstate->null_print) == 0 )
! 				{
! 					/*
! 					 * FORCE_NULL option is set and column matches the NULL string.
! 					 * It must have been quoted, or otherwise the string would already
! 					 * have been set to NULL.
! 					 * Convert it to NULL as specified.
! 					 */
! 					string = NULL;
! 				}
  			}
  
  			cstate->cur_attname = NameStr(attr[m]->attname);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 81169a4..e3060a4
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
*************** copy_opt_item:
*** 2548,2553 ****
--- 2548,2557 ----
  				{
  					$$ = makeDefElem("force_not_null", (Node *)$4);
  				}
+ 			| FORCE NULL_P columnList
+ 				{
+ 					$$ = makeDefElem("force_null", (Node *)$3);
+ 				}
  			| ENCODING Sconst
  				{
  					$$ = makeDefElem("encoding", (Node *)makeString($2));
diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
new file mode 100644
index 34fa131..de99108
*** a/src/test/regress/expected/copy2.out
--- b/src/test/regress/expected/copy2.out
*************** SELECT * FROM vistest;
*** 382,387 ****
--- 382,435 ----
   e
  (2 rows)
  
+ -- Test FORCE_NOT_NULL and FORCE_NULL options
+ -- should succeed with "b" set to an empty string and "c" set to NULL
+ CREATE TEMP TABLE forcetest (
+     a INT NOT NULL,
+     b TEXT NOT NULL,
+     c TEXT,
+     d TEXT,
+     e TEXT
+ );
+ \pset null NULL
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 1;
+  b |  c   
+ ---+------
+    | NULL
+ (1 row)
+ 
+ -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 2;
+  b |  c   
+ ---+------
+    | NULL
+ (1 row)
+ 
+ -- should fail with not-null constraint violiaton
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ ERROR:  null value in column "b" violates not-null constraint
+ DETAIL:  Failing row contains (3, null, , null, null).
+ CONTEXT:  COPY forcetest, line 1: "3,,"""
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ ERROR:  FORCE NOT NULL column "b" not referenced by COPY
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ ERROR:  FORCE NULL column "b" not referenced by COPY
+ ROLLBACK;
+ \pset null ''
+ DROP TABLE forcetest;
  DROP TABLE vistest;
  DROP FUNCTION truncate_in_subxact();
  DROP TABLE x, y;
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
new file mode 100644
index c46128b..b417cf7
*** a/src/test/regress/sql/copy2.sql
--- b/src/test/regress/sql/copy2.sql
*************** e
*** 270,275 ****
--- 270,314 ----
  SELECT * FROM vistest;
  COMMIT;
  SELECT * FROM vistest;
+ -- Test FORCE_NOT_NULL and FORCE_NULL options
+ -- should succeed with "b" set to an empty string and "c" set to NULL
+ CREATE TEMP TABLE forcetest (
+     a INT NOT NULL,
+     b TEXT NOT NULL,
+     c TEXT,
+     d TEXT,
+     e TEXT
+ );
+ \pset null NULL
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ 1,,""
+ \.
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 1;
+ -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+ 2,,""
+ \.
+ COMMIT;
+ SELECT b, c FROM forcetest WHERE a = 2;
+ -- should fail with not-null constraint violiaton
+ BEGIN;
+ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));
+ 3,,""
+ \.
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
+ ROLLBACK;
+ -- should fail with "not referenced by COPY" error
+ BEGIN;
+ COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b));
+ ROLLBACK;
+ \pset null ''
+ DROP TABLE forcetest;
  DROP TABLE vistest;
  DROP FUNCTION truncate_in_subxact();
  DROP TABLE x, y;

diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
index 76dea28..e8fb3d1 100644
--- a/src/test/regress/expected/copy2.out
+++ b/src/test/regress/expected/copy2.out
@@ -383,7 +383,6 @@ SELECT * FROM vistest;
 (2 rows)
 
 -- Test FORCE_NOT_NULL and FORCE_NULL options
--- should succeed with "b" set to an empty string and "c" set to NULL
 CREATE TEMP TABLE forcetest (
     a INT NOT NULL,
     b TEXT NOT NULL,
@@ -392,6 +391,7 @@ CREATE TEMP TABLE forcetest (
     e TEXT
 );
 \pset null NULL
+-- should succeed with "b" set to an empty string and "c" set to NULL
 BEGIN;
 COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
 COMMIT;
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
index e2be21f..63332bd 100644
--- a/src/test/regress/sql/copy2.sql
+++ b/src/test/regress/sql/copy2.sql
@@ -271,7 +271,6 @@ SELECT * FROM vistest;
 COMMIT;
 SELECT * FROM vistest;
 -- Test FORCE_NOT_NULL and FORCE_NULL options
--- should succeed with "b" set to an empty string and "c" set to NULL
 CREATE TEMP TABLE forcetest (
     a INT NOT NULL,
     b TEXT NOT NULL,
@@ -280,6 +279,7 @@ CREATE TEMP TABLE forcetest (
     e TEXT
 );
 \pset null NULL
+-- should succeed with "b" set to an empty string and "c" set to NULL
 BEGIN;
 COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
 1,,""
@@ -289,7 +289,7 @@ SELECT b, c FROM forcetest WHERE a = 1;
 -- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
 BEGIN;
 COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
-2,,""
+2,"",
 \.
 COMMIT;
 SELECT b, c FROM forcetest WHERE a = 2;

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 70ee7e5..540da91 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -1457,6 +1457,26 @@ BeginCopy(bool is_from,
 		}
 	}
 
+	/*
+	 * Check if both force_null and force_not_null are used on the same
+	 * columns.
+	 */
+	if (cstate->force_null && cstate->force_notnull)
+	{
+		int i;
+
+		for (i = 0; i < num_phys_attrs; i++)
+		{
+			if (cstate->force_notnull_flags[i] &&
+				cstate->force_null_flags[i])
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 errhint("\"force_not_null\" and \"force_null\" specified for the same column \"%s\"",
+								 NameStr(tupDesc->attrs[i]->attname))));
+		}
+	}
+
 	/* Use client encoding when ENCODING option is not specified. */
 	if (cstate->file_encoding < 0)
 		cstate->file_encoding = pg_get_client_encoding();
diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
index 76dea28..5341b09 100644
--- a/src/test/regress/expected/copy2.out
+++ b/src/test/regress/expected/copy2.out
@@ -418,6 +418,12 @@ ERROR:  null value in column "b" violates not-null constraint
 DETAIL:  Failing row contains (3, null, , null, null).
 CONTEXT:  COPY forcetest, line 1: "3,,"""
 ROLLBACK;
+-- FORCE_NULL and FORCE_NOT_NULL cannot be used on the same column
+BEGIN;
+COPY forcetest (a) FROM STDIN WITH (FORMAT csv, FORCE_NULL(a), FORCE_NOT_NULL(a));
+ERROR:  conflicting or redundant options
+HINT:  "force_not_null" and "force_null" specified for the same column "a"
+ROLLBACK;
 -- should fail with "not referenced by COPY" error
 BEGIN;
 COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
index e2be21f..91dc902 100644
--- a/src/test/regress/sql/copy2.sql
+++ b/src/test/regress/sql/copy2.sql
@@ -299,6 +299,10 @@ COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_N
 3,,""
 \.
 ROLLBACK;
+-- FORCE_NULL and FORCE_NOT_NULL cannot be used on the same column
+BEGIN;
+COPY forcetest (a) FROM STDIN WITH (FORMAT csv, FORCE_NULL(a), FORCE_NOT_NULL(a));
+ROLLBACK;
 -- should fail with "not referenced by COPY" error
 BEGIN;
 COPY forcetest (d, e) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b));

diff --git a/contrib/file_fdw/file_fdw.c b/contrib/file_fdw/file_fdw.c
index 7fb1dbc..97a35d0 100644
--- a/contrib/file_fdw/file_fdw.c
+++ b/contrib/file_fdw/file_fdw.c
@@ -267,11 +267,6 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options"),
 						 errhint("option \"force_not_null\" supplied more than once for a column")));
-			if(force_null)
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("conflicting or redundant options"),
-						 errhint("option \"force_not_null\" cannot be used together with \"force_null\"")));
 			force_not_null = def;
 			/* Don't care what the value is, as long as it's a legal boolean */
 			(void) defGetBoolean(def);
@@ -284,11 +279,6 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options"),
 						 errhint("option \"force_null\" supplied more than once for a column")));
-			if(force_not_null)
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("conflicting or redundant options"),
-						 errhint("option \"force_null\" cannot be used together with \"force_not_null\"")));
 			force_null = def;
 			(void) defGetBoolean(def);
 		}
diff --git a/contrib/file_fdw/input/file_fdw.source b/contrib/file_fdw/input/file_fdw.source
index 0c278aa..b608372 100644
--- a/contrib/file_fdw/input/file_fdw.source
+++ b/contrib/file_fdw/input/file_fdw.source
@@ -91,24 +91,22 @@ ALTER FOREIGN TABLE text_csv OPTIONS (SET format 'csv');
 \pset null _null_
 SELECT * FROM text_csv;
 
+-- force_not_null and force_null can be used together on the same column
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true');
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true');
+
 -- force_not_null is not allowed to be specified at any foreign object level:
 ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_not_null '*'); -- ERROR
 ALTER SERVER file_server OPTIONS (ADD force_not_null '*'); -- ERROR
 CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
 
--- force_not_null cannot be specified together with force_null
-ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
-
 -- force_null is not allowed to be specified at any foreign object level:
 ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
 ALTER SERVER file_server OPTIONS (ADD force_null '*'); -- ERROR
 CREATE USER MAPPING FOR public SERVER file_server OPTIONS (force_null '*'); -- ERROR
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
 
--- force_null cannot be specified together with force_not_null
-ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
-
 -- basic query tests
 SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
 SELECT * FROM agg_csv ORDER BY a;
diff --git a/contrib/file_fdw/output/file_fdw.source b/contrib/file_fdw/output/file_fdw.source
index 2bec160..bc183b8 100644
--- a/contrib/file_fdw/output/file_fdw.source
+++ b/contrib/file_fdw/output/file_fdw.source
@@ -115,6 +115,9 @@ SELECT * FROM text_csv;
  ABC   | abc    |        | 
 (5 rows)
 
+-- force_not_null and force_null can be used together on the same column
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true');
+ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true');
 -- force_not_null is not allowed to be specified at any foreign object level:
 ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_not_null '*'); -- ERROR
 ERROR:  invalid option "force_not_null"
@@ -128,10 +131,6 @@ HINT:  There are no valid options in this context.
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_not_null '*'); -- ERROR
 ERROR:  invalid option "force_not_null"
 HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
--- force_not_null cannot be specified together with force_null
-ALTER FOREIGN TABLE text_csv ALTER COLUMN word1 OPTIONS (force_null 'true'); --ERROR
-ERROR:  conflicting or redundant options
-HINT:  option "force_null" cannot be used together with "force_not_null"
 -- force_null is not allowed to be specified at any foreign object level:
 ALTER FOREIGN DATA WRAPPER file_fdw OPTIONS (ADD force_null '*'); -- ERROR
 ERROR:  invalid option "force_null"
@@ -145,10 +144,6 @@ HINT:  There are no valid options in this context.
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (force_null '*'); -- ERROR
 ERROR:  invalid option "force_null"
 HINT:  Valid options in this context are: filename, format, header, delimiter, quote, escape, null, encoding
--- force_null cannot be specified together with force_not_null
-ALTER FOREIGN TABLE text_csv ALTER COLUMN word3 OPTIONS (force_not_null 'true'); --ERROR
-ERROR:  conflicting or redundant options
-HINT:  option "force_not_null" cannot be used together with "force_null"
 -- basic query tests
 SELECT * FROM agg_text WHERE b > 10.0 ORDER BY a;
   a  |   b    

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 5be3514..13cd528 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -477,6 +477,13 @@ COPY <replaceable class="parameter">count</replaceable>
     <command>VACUUM</command> to recover the wasted space.
    </para>
 
+   <para>
+    <literal>FORCE_NULL</> and <literal>FORCE_NOT_NULL</> can be used
+    simultaneously on the same column. This has as result to convert quoted
+    null strings to null values and to convert unquoted null strings to
+    empty strings.
+   </para>
+
  </refsect1>
 
  <refsect1>
diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
index 76dea28..035d843 100644
--- a/src/test/regress/expected/copy2.out
+++ b/src/test/regress/expected/copy2.out
@@ -383,7 +383,6 @@ SELECT * FROM vistest;
 (2 rows)
 
 -- Test FORCE_NOT_NULL and FORCE_NULL options
--- should succeed with "b" set to an empty string and "c" set to NULL
 CREATE TEMP TABLE forcetest (
     a INT NOT NULL,
     b TEXT NOT NULL,
@@ -392,6 +391,7 @@ CREATE TEMP TABLE forcetest (
     e TEXT
 );
 \pset null NULL
+-- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
 BEGIN;
 COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
 COMMIT;
@@ -401,12 +401,12 @@ SELECT b, c FROM forcetest WHERE a = 1;
    | NULL
 (1 row)
 
--- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+-- should succeed, FORCE_NULL and FORCE_NOT_NULL can be both specified
 BEGIN;
-COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
+COPY forcetest (a, b, c, d) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(c,d), FORCE_NULL(c,d));
 COMMIT;
-SELECT b, c FROM forcetest WHERE a = 2;
- b |  c   
+SELECT c, d FROM forcetest WHERE a = 2;
+ c |  d   
 ---+------
    | NULL
 (1 row)
diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
index e2be21f..248055f 100644
--- a/src/test/regress/sql/copy2.sql
+++ b/src/test/regress/sql/copy2.sql
@@ -271,7 +271,6 @@ SELECT * FROM vistest;
 COMMIT;
 SELECT * FROM vistest;
 -- Test FORCE_NOT_NULL and FORCE_NULL options
--- should succeed with "b" set to an empty string and "c" set to NULL
 CREATE TEMP TABLE forcetest (
     a INT NOT NULL,
     b TEXT NOT NULL,
@@ -280,19 +279,20 @@ CREATE TEMP TABLE forcetest (
     e TEXT
 );
 \pset null NULL
+-- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
 BEGIN;
 COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
 1,,""
 \.
 COMMIT;
 SELECT b, c FROM forcetest WHERE a = 1;
--- should succeed with no effect ("b" remains an empty string, "c" remains NULL)
+-- should succeed, FORCE_NULL and FORCE_NOT_NULL can be both specified
 BEGIN;
-COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(b), FORCE_NULL(c));
-2,,""
+COPY forcetest (a, b, c, d) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(c,d), FORCE_NULL(c,d));
+2,'a',,""
 \.
 COMMIT;
-SELECT b, c FROM forcetest WHERE a = 2;
+SELECT c, d FROM forcetest WHERE a = 2;
 -- should fail with not-null constraint violation
 BEGIN;
 COPY forcetest (a, b, c) FROM STDIN WITH (FORMAT csv, FORCE_NULL(b), FORCE_NOT_NULL(c));