Using \copy to populate a table

Have you tried explicitly specifying the string to represent null values?

COPY table_name FROM 'path/to/file' WITH (FORMAT text, NULL 'null');
-- Or the older syntax:
COPY table_name FROM 'path/to/file' WITH DELIMITER ',' NULL AS 'null';

________________________________
From: rob stone <floriparob@tpg.com.au>
Sent: Sunday, March 15, 2026 8:11 PM
To: PostGreSQL MailingList <pgsql-general@postgresql.org>
Subject: Using \copy to populate a table

psql (18.3 (Debian 18.3-1+b1))
Type "help" for help.

Debian OS is forky.

When setting up a new development database, the following occurred:-

applntestdb=> \copy forms_table (item_type, navgn_refn, html_name,
table_key, navgn_bar, rows_page, forward_to, second_to, tertiary_to,
active_item, super_only, system_admin, inserted_by) from
'/home/postgres/loadfiles/formstable.txt' header delimiter '|';
ERROR: invalid input syntax for type smallint: "null"
CONTEXT: COPY forms_table, line 2, column rows_page: "null"
applntestdb=>

This is what is on line 2 of the file:-
C|0|pageloader|||null|null|null|null|t|f|f|0

The test below was simplified to just choose one SMALLINT column.

applntestdb=> insert into forms_table (item_type, navgn_refn,
html_name, rows_page, active_item,
inserted_by) values ('C', 0, 'pageloader', null, TRUE, 0);
INSERT 0 1
applntestdb=> delete from forms_table where item_type = 'C';
DELETE 1
applntestdb=> insert into forms_table (item_type, navgn_refn,
html_name, rows_page, active_item,
inserted_by) values ('C', 0, 'pageloader', '', TRUE, 0);
ERROR: invalid input syntax for type smallint: ""
LINE 2: inserted_by) values ('C', 0, 'pageloader', '', TRUE, 0)
^

So, psql is quite happy to insert null into a column defined as
smallint, but when you use the \copy mechanism to populate a table it
pulls an error.

How do we fix this? Alter all the nulls to zeroes in the file or write
a program to dissect the file and create individual insert statements?

Has anybody else had this problem and if so what was the solution?

Thanks,
Rob

Brent Wood
Principal Technician - GIS and Spatial Data Management
+64-4-386-0529
301 Evans Bay Parade, Greta Point, Hataitai, Wellington, New Zealand
Earth Sciences New Zealand
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On Sun, Mar 15, 2026 at 3:12 AM rob stone <floriparob@tpg.com.au> wrote:

psql (18.3 (Debian 18.3-1+b1))
Type "help" for help.

Debian OS is forky.

When setting up a new development database, the following occurred:-

applntestdb=> \copy forms_table (item_type, navgn_refn, html_name,
table_key, navgn_bar, rows_page, forward_to, second_to, tertiary_to,
active_item, super_only, system_admin, inserted_by) from
'/home/postgres/loadfiles/formstable.txt' header delimiter '|';
ERROR: invalid input syntax for type smallint: "null"
CONTEXT: COPY forms_table, line 2, column rows_page: "null"
applntestdb=>

This is what is on line 2 of the file:-
C|0|pageloader|||null|null|null|null|t|f|f|0

The test below was simplified to just choose one SMALLINT column.

applntestdb=> insert into forms_table (item_type, navgn_refn,
html_name, rows_page, active_item,
inserted_by) values ('C', 0, 'pageloader', null, TRUE, 0);
INSERT 0 1
applntestdb=> delete from forms_table where item_type = 'C';
DELETE 1
applntestdb=> insert into forms_table (item_type, navgn_refn,
html_name, rows_page, active_item,
inserted_by) values ('C', 0, 'pageloader', '', TRUE, 0);
ERROR: invalid input syntax for type smallint: ""
LINE 2: inserted_by) values ('C', 0, 'pageloader', '', TRUE, 0)
^

So, psql is quite happy to insert null into a column defined as
smallint, but when you use the \copy mechanism to populate a table it
pulls an error.

How do we fix this? Alter all the nulls to zeroes in the file or write
a program to dissect the file and create individual insert statements?

Has anybody else had this problem and if so what was the solution?

"null" is not what COPY uses to signal a null value. I think it's \N but
the best solution i to COPY TO your table to STDOUT and see what it uses as
the null indicator.
\copy forms_table TO STDOUT WITH (HEADER, DELIMITER '|');

--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

Hi Rob:

On Sun, 15 Mar 2026 at 08:12, rob stone <floriparob@tpg.com.au> wrote:

This is what is on line 2 of the file:-
C|0|pageloader|||null|null|null|null|t|f|f|0

...

So, psql is quite happy to insert null into a column defined as
smallint, but when you use the \copy mechanism to populate a table it
pulls an error.

It does not for me, but syntax for INSERT and COPY ( \copy just does a COPY
from stdin ) is different.

How do we fix this? Alter all the nulls to zeroes in the file or write
a program to dissect the file and create individual insert statements?

Have you tried a little RTFM?

specifically ....

https://www.postgresql.org/docs/18/sql-copy.html

Where somewhere it says:

NULL

Specifies the string that represents a null value. The default is \N
(backslash-N) in text format, and an unquoted empty string in CSV format.
You might prefer an empty string even in text format for cases where you
don't want to distinguish nulls from empty strings. This option is not
allowed when using binary format.

If you generate four text files I would recommend switching to \N, it will
be less painful.

Francisco Olarte.

On 3/15/26 12:11 AM, rob stone wrote:

psql (18.3 (Debian 18.3-1+b1))
Type "help" for help.

Debian OS is forky.

When setting up a new development database, the following occurred:-

How do we fix this? Alter all the nulls to zeroes in the file or write
a program to dissect the file and create individual insert statements?

CSV is a text format and in:

C|0|pageloader|||null|null|null|null|t|f|f|0

the null values are the string 'null' which indeed is not a valid syntax
for a smallint.

Has anybody else had this problem and if so what was the solution?

Do you have control over whatever creates the file?

An option is to create a staging table that is has all string fields,
import into it and then do clean up before moving to final table.

Thanks,
Rob

--
Adrian Klaver
adrian.klaver@aklaver.com

On Sun, Mar 15, 2026 at 3:12 AM rob stone <floriparob@tpg.com.au> wrote:

psql (18.3 (Debian 18.3-1+b1))
Type "help" for help.

Debian OS is forky.

When setting up a new development database, the following occurred:-

applntestdb=> \copy forms_table (item_type, navgn_refn, html_name,
table_key, navgn_bar, rows_page, forward_to, second_to, tertiary_to,
active_item, super_only, system_admin, inserted_by) from
'/home/postgres/loadfiles/formstable.txt' header delimiter '|';
ERROR: invalid input syntax for type smallint: "null"
CONTEXT: COPY forms_table, line 2, column rows_page: "null"
applntestdb=>

This is what is on line 2 of the file:-
C|0|pageloader|||null|null|null|null|t|f|f|0

The test below was simplified to just choose one SMALLINT column.

applntestdb=> insert into forms_table (item_type, navgn_refn,
html_name, rows_page, active_item,
inserted_by) values ('C', 0, 'pageloader', null, TRUE, 0);
INSERT 0 1
applntestdb=> delete from forms_table where item_type = 'C';
DELETE 1
applntestdb=> insert into forms_table (item_type, navgn_refn,
html_name, rows_page, active_item,
inserted_by) values ('C', 0, 'pageloader', '', TRUE, 0);
ERROR: invalid input syntax for type smallint: ""
LINE 2: inserted_by) values ('C', 0, 'pageloader', '', TRUE, 0)
^

So, psql is quite happy to insert null into a column defined as
smallint, but when you use the \copy mechanism to populate a table it
pulls an error.

How do we fix this? Alter all the nulls to zeroes in the file or write
a program to dissect the file and create individual insert statements?

Has anybody else had this problem and if so what was the solution?

Caveat: I'm a hack, I rarely respond to questions here, I have limited
knowledge about PGSQL, databases in general, and generally hesitate to
chime in where my betters are wont to dwell.

That said... If it was me, I would at least try switching this

\copy forms_table (item_type, navgn_refn, html_name,
table_key, navgn_bar, rows_page, forward_to, second_to, tertiary_to,
active_item, super_only, system_admin, inserted_by) from
'/home/postgres/loadfiles/formstable.txt' header delimiter '|';

with this

\copy forms_table (item_type, navgn_refn, html_name,
table_key, navgn_bar, rows_page, forward_to, second_to, tertiary_to,
active_item, super_only, system_admin, inserted_by) from
'/home/postgres/loadfiles/formstable.txt' with header delimiter '|' NULL as
'null';

In other words, your CSV file seems to be outputting the string 'null' for
NULL values.

Doing it this way, however, would mean that any of your fields whose string
values might be "null" would be interpreted as NULL values.

The fact that no one has already offered this as an approach makes me
skeptical, but perhaps you could give it a shot to see if it works.

Pete

On Sun, 2026-03-15 at 07:21 +0000, Brent Wood wrote:

Have you tried explicitly specifying the string to represent null
values?

COPY table_name FROM 'path/to/file' WITH (FORMAT text, NULL 'null');
-- Or the older syntax:
COPY table_name FROM 'path/to/file' WITH DELIMITER ',' NULL AS
'null';

Hello,

I took on board Adrian's suggestion and went back to the source and had
the file recreated and it has now been loaded successfully.

Cheers,
Rob