cursors and function question

On Tuesday, February 13, 2018, armand pirvu <armand.pirvu@gmail.com> wrote:

CREATE OR REPLACE FUNCTION foofunc()
RETURNS text AS $$

select foofunc();
foofunc
-------------------------------
("E1 ","CAT1 ",0)

But I am looking to get

foofunc
-------------------------------
("E1 ","CAT1 ",0)
("E1 ","CATs ",0)

You need to specify SETOF

CREATE FUNCTION foofunc() RETURNS SETOF text AS

David J.

On 02/13/2018 10:22 AM, armand pirvu wrote:

Hi

Is there any elegant way not a two steps way I can output the cursor value at each step?

testtbl table has this content

col1 | col2 | col3
------------+------------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0

This works
BEGIN WORK;
DECLARE fooc CURSOR FOR SELECT * FROM testtbl;
FETCH ALL FROM fooc;
CLOSE fooc;
COMMIT WORK;

col1 | col2 | col3
------------+------------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0

But
CREATE OR REPLACE FUNCTION foofunc()
RETURNS text AS $$
DECLARE
var2 RECORD;
cur CURSOR FOR SELECT * from testtbl;
BEGIN
OPEN cur;
LOOP
FETCH cur INTO var2;
return var2;
END LOOP;
CLOSE cur;
END; $$
LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION public.foofunc()
RETURNS SETOF testtbl
LANGUAGE sql
AS $function$
SELECT * FROM testtbl;
$function$

test=> select * from foofunc();
col1 | col2 | col3
------+------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
(7 rows)

select foofunc();
foofunc
-------------------------------
("E1 ","CAT1 ",0)

But I am looking to get

foofunc
-------------------------------
("E1 ","CAT1 ",0)
("E1 ","CATs ",0)
etc

Many thanks
— Armand

--
Adrian Klaver
adrian.klaver@aklaver.com

On Feb 13, 2018, at 12:26 PM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Tuesday, February 13, 2018, armand pirvu <armand.pirvu@gmail.com <mailto:armand.pirvu@gmail.com>> wrote:

CREATE OR REPLACE FUNCTION foofunc()
RETURNS text AS $$

select foofunc();
foofunc
-------------------------------
("E1 ","CAT1 ",0)

But I am looking to get

foofunc
-------------------------------
("E1 ","CAT1 ",0)
("E1 ","CATs ",0)

You need to specify SETOF

CREATE FUNCTION foofunc() RETURNS SETOF text AS

David J.

Thank you but

CREATE OR REPLACE FUNCTION foofunc()
RETURNS setof text AS $$
DECLARE
var2 RECORD;
cur CURSOR FOR SELECT * from testtbl;
BEGIN
OPEN cur;
LOOP
FETCH cur INTO var2;
return var2;
END LOOP;
CLOSE cur;
END; $$
LANGUAGE plpgsql;

ERROR: RETURN cannot have a parameter in function returning set
LINE 10: return var2;
HINT: Use RETURN NEXT or RETURN QUERY.

so I employed next

CREATE OR REPLACE FUNCTION foofunc()
RETURNS setof text AS $$
DECLARE
var2 text;
cur CURSOR FOR SELECT col1 from testtbl;
BEGIN
OPEN cur;
LOOP
FETCH cur INTO var2;
return next var2;
END LOOP;
CLOSE cur;
END; $$
LANGUAGE plpgsql;

and it just sits there

Any hints ?

Thank you
— Armand

On Tue, Feb 13, 2018 at 12:03 PM, armand pirvu <armand.pirvu@gmail.com>
wrote:

ERROR: RETURN cannot have a parameter in function returning set
LINE 10: return var2;
HINT: Use RETURN NEXT or RETURN QUERY.

and it just sits there

Any hints ?

https://www.postgresql.org/docs/10/static/plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING
​

David J.

On Feb 13, 2018, at 12:54 PM, Adrian Klaver <adrian.klaver@aklaver.com> wrote:

On 02/13/2018 10:22 AM, armand pirvu wrote:

Hi
Is there any elegant way not a two steps way I can output the cursor value at each step?
testtbl table has this content
col1 | col2 | col3
------------+------------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
This works
BEGIN WORK;
DECLARE fooc CURSOR FOR SELECT * FROM testtbl;
FETCH ALL FROM fooc;
CLOSE fooc;
COMMIT WORK;
col1 | col2 | col3
------------+------------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
But
CREATE OR REPLACE FUNCTION foofunc()
RETURNS text AS $$
DECLARE
var2 RECORD;
cur CURSOR FOR SELECT * from testtbl;
BEGIN
OPEN cur;
LOOP
FETCH cur INTO var2;
return var2;
END LOOP;
CLOSE cur;
END; $$
LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION public.foofunc()
RETURNS SETOF testtbl
LANGUAGE sql
AS $function$
SELECT * FROM testtbl;
$function$

test=> select * from foofunc();
col1 | col2 | col3
------+------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
(7 rows)

select foofunc();
foofunc
-------------------------------
("E1 ","CAT1 ",0)
But I am looking to get
foofunc
-------------------------------
("E1 ","CAT1 ",0)
("E1 ","CATs ",0)
etc
Many thanks
— Armand

--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

Thanks Adrian

That one I figured it out as well. The idea is that said table has some records which I need to loop and do some processing using cursors similar with

DECLARE
cur CURSOR FOR SELECT *
FROM testtbl FOR UPDATE;
BEGIN
FOR row IN cur LOOP
UPDATE testtbl
SET col3=1
WHERE CURRENT OF cur;
END LOOP;
return cur;
END

For a row update the goal is to return the cursor value be it before/after the update, hence my question and test

I found some code which seems to do what I need but it involves two functions

CREATE or replace FUNCTION reffunc(refcursor) RETURNS refcursor AS $$
BEGIN
OPEN $1 FOR SELECT col FROM test;
RETURN $1;
END;
$$ LANGUAGE plpgsql;

BEGIN;
SELECT reffunc('funccursor');
FETCH ALL IN funccursor;
COMMIT;

And this is what beats me , aka can I put all in one / how ?

Thanks
Armand

On 02/13/2018 11:17 AM, armand pirvu wrote:

On Feb 13, 2018, at 12:54 PM, Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:

On 02/13/2018 10:22 AM, armand pirvu wrote:

Hi
Is there any elegant way not a two steps way I can output the cursor
value at each step?
testtbl table has this content
    col1    |    col2    | col3
------------+------------+------
 E1         | CAT1       |    0
 E1         | CAT2       |    0
 E1         | CAT3       |    0
 E4         | CAT1       |    0
 E5         | CAT1       |    0
 E6         | CAT1       |    0
 E7         | CAT1       |    0
This works
BEGIN WORK;
DECLARE fooc  CURSOR FOR SELECT * FROM testtbl;
FETCH ALL FROM fooc;
CLOSE fooc;
COMMIT WORK;
    col1    |    col2    | col3
------------+------------+------
 E1         | CAT1       |    0
 E1         | CAT2       |    0
 E1         | CAT3       |    0
 E4         | CAT1       |    0
 E5         | CAT1       |    0
 E6         | CAT1       |    0
 E7         | CAT1       |    0
But
CREATE OR REPLACE FUNCTION foofunc()
   RETURNS text AS $$
DECLARE
 var2   RECORD;
 cur CURSOR FOR SELECT * from testtbl;
BEGIN
   OPEN cur;
    LOOP
      FETCH cur INTO var2;
      return var2;
   END LOOP;
   CLOSE cur;
END; $$
LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION public.foofunc()
RETURNS SETOF testtbl
LANGUAGE sql
AS $function$
   SELECT * FROM testtbl;
$function$

test=> select * from foofunc();
col1 | col2 | col3
------+------+------
E1   | CAT1 |    0
E1   | CAT2 |    0
E1   | CAT3 |    0
E4   | CAT1 |    0
E5   | CAT1 |    0
E6   | CAT1 |    0
E7   | CAT1 |    0
(7 rows)

select foofunc();
            foofunc
-------------------------------
 ("E1        ","CAT1      ",0)
But I am looking to get
            foofunc
-------------------------------
 ("E1        ","CAT1      ",0)
 ("E1        ","CATs      ",0)
etc
Many thanks
— Armand

--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

Thanks Adrian

That one I figured it out as well. The idea is that said table has some
records which I need to loop and do some processing using cursors
similar with

DECLARE
cur CURSOR FOR SELECT *
    FROM testtbl FOR UPDATE;
BEGIN
  FOR row IN cur LOOP
    UPDATE testtbl
    SET col3=1
    WHERE CURRENT OF cur;
  END LOOP;
  return cur;
END

For a row update the goal is to return the cursor value  be it
before/after the update, hence my question and test

Not following, are you looking to do this in an UPDATE trigger or
somewhere else?

Another way to ask is why do you want to use a cursor?

I found some code which seems to do what I need but it involves two
functions
CREATE or replace FUNCTION reffunc(refcursor) RETURNS refcursor AS $$
BEGIN
    OPEN $1 FOR SELECT col FROM test;
    RETURN $1;
END;
$$ LANGUAGE plpgsql;

BEGIN;
SELECT reffunc('funccursor');
FETCH ALL IN funccursor;
COMMIT;

And this is what beats  me , aka can I put all in one / how ?

Thanks
Armand

--
Adrian Klaver
adrian.klaver@aklaver.com

On Feb 13, 2018, at 1:22 PM, Adrian Klaver <adrian.klaver@aklaver.com> wrote:

On 02/13/2018 11:17 AM, armand pirvu wrote:

On Feb 13, 2018, at 12:54 PM, Adrian Klaver <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com><mailto:adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>>> wrote:

On 02/13/2018 10:22 AM, armand pirvu wrote:

Hi
Is there any elegant way not a two steps way I can output the cursor value at each step?
testtbl table has this content
col1 | col2 | col3
------------+------------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
This works
BEGIN WORK;
DECLARE fooc CURSOR FOR SELECT * FROM testtbl;
FETCH ALL FROM fooc;
CLOSE fooc;
COMMIT WORK;
col1 | col2 | col3
------------+------------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
But
CREATE OR REPLACE FUNCTION foofunc()
RETURNS text AS $$
DECLARE
var2 RECORD;
cur CURSOR FOR SELECT * from testtbl;
BEGIN
OPEN cur;
LOOP
FETCH cur INTO var2;
return var2;
END LOOP;
CLOSE cur;
END; $$
LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION public.foofunc()
RETURNS SETOF testtbl
LANGUAGE sql
AS $function$
SELECT * FROM testtbl;
$function$

test=> select * from foofunc();
col1 | col2 | col3
------+------+------
E1 | CAT1 | 0
E1 | CAT2 | 0
E1 | CAT3 | 0
E4 | CAT1 | 0
E5 | CAT1 | 0
E6 | CAT1 | 0
E7 | CAT1 | 0
(7 rows)

select foofunc();
foofunc
-------------------------------
("E1 ","CAT1 ",0)
But I am looking to get
foofunc
-------------------------------
("E1 ","CAT1 ",0)
("E1 ","CATs ",0)
etc
Many thanks
— Armand

--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com> <mailto:adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>>

Thanks Adrian
That one I figured it out as well. The idea is that said table has some records which I need to loop and do some processing using cursors similar with
DECLARE
cur CURSOR FOR SELECT *
FROM testtbl FOR UPDATE;
BEGIN
FOR row IN cur LOOP
UPDATE testtbl
SET col3=1
WHERE CURRENT OF cur;
END LOOP;
return cur;
END
For a row update the goal is to return the cursor value be it before/after the update, hence my question and test

Not following, are you looking to do this in an UPDATE trigger or somewhere else?

Another way to ask is why do you want to use a cursor?

I found some code which seems to do what I need but it involves two functions
CREATE or replace FUNCTION reffunc(refcursor) RETURNS refcursor AS $$
BEGIN
OPEN $1 FOR SELECT col FROM test;
RETURN $1;
END;
$$ LANGUAGE plpgsql;
BEGIN;
SELECT reffunc('funccursor');
FETCH ALL IN funccursor;
COMMIT;
And this is what beats me , aka can I put all in one / how ?
Thanks
Armand

--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

Not a trigger , but the idea is we will do some batch processing from said table let’s name it testtbl

1 - we get the records using select for update with a limit 100 for example
2 - update each record using using cursor
3 - print the cursor content so that way I have an idea what was updated

I was thinking that if I can put a unique constraint on the table, I can generate a global table in the function , update main table from global table and return select from global table

I can see the developer desire to use cursors to minimize some effort on his side

Thanks

Armand

On 02/13/2018 01:25 PM, armand pirvu wrote:

On Feb 13, 2018, at 1:22 PM, Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:

Not a trigger , but the idea is we will do some batch processing from
said table let’s name it testtbl

1 - we get the records using  select for update with a limit 100 for example
2 - update each record using using cursor
3 - print the cursor content so that way I have an idea what was updated

I was thinking that if I can put a unique constraint on the table, I can
generate a global table in the function , update main table from global
table and return select from global table

Not entirely sure I know what you are trying to accomplish, still:

1) Not sure you need to use cursor, see here for less complicated way:

https://www.postgresql.org/docs/10/static/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING

and

https://www.postgresql.org/docs/10/static/plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING

Using RETURN NEXT.

Keeping mind:

https://www.postgresql.org/docs/10/static/plpgsql-cursors.html
"Rather than executing a whole query at once, it is possible to set up a
cursor that encapsulates the query, and then read the query result a few
rows at a time. One reason for doing this is to avoid memory overrun
when the result contains a large number of rows. (However, PL/pgSQL
users do not normally need to worry about that, since FOR loops
automatically use a cursor internally to avoid memory problems.) A more
interesting usage is to return a reference to a cursor that a function
has created, allowing the caller to read the rows. This provides an
efficient way to return large row sets from functions."

So if you are keeping the rows to 100 a FOR loop would seem to suffice.

2) By global table do you mean a temporary table? If so not sure that is
going to work as I am pretty sure it will disappear after the function
is run. I could see having a permanent table that you INSERT the updated
rows into with a timestamp. Then you could update the main table from
that and prune old records using the timestamps.

I can see the developer desire to use cursors to minimize some effort on
his side

Thanks

Armand

--
Adrian Klaver
adrian.klaver@aklaver.com

On Tue, Feb 13, 2018 at 3:31 PM, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:

2) By global table do you mean a temporary table? If so not sure that is
going to work as I am pretty sure it will disappear after the function is
run.

​Temporary tables can survive until either session or transaction end -
neither of which occurs automatically when exiting a function.

https://www.postgresql.org/docs/10/static/sql-createtable.html

"Temporary tables are automatically dropped at the end of a session, or
optionally at the end of the current transaction (see ON COMMIT below)"

David J.

On Feb 13, 2018, at 4:37 PM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Tue, Feb 13, 2018 at 3:31 PM, Adrian Klaver <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>> wrote:
2) By global table do you mean a temporary table? If so not sure that is going to work as I am pretty sure it will disappear after the function is run.

​Temporary tables can survive until either session or transaction end - neither of which occurs automatically when exiting a function.

https://www.postgresql.org/docs/10/static/sql-createtable.html <https://www.postgresql.org/docs/10/static/sql-createtable.html&gt;

"Temporary tables are automatically dropped at the end of a session, or optionally at the end of the current transaction (see ON COMMIT below)"

David J.

Thank you both of you Adrian and David for the input and help

I owe you some nice red wine :)

Cheers
- Armand