Re : Getting results from a dynamic query in PL/pgSQL

Alain RICHARD wrote:

Look at chapter 19.6.4 Looping through query results.

i.e using plpgsql language:
DECLARE
myRecord RECORD
BEGIN
...
FOR myRecord IN EXECUTE ''SELECT col1, col2 FROM myTable '' LOOP
-- statements using myRecord.col1 and myRecord.col2 ;
END LOOP;
...
END;
FOR

Thank You Alain and Tom for Your replies.
That function works well when the name of the column is known. However,
I do not always know the column name.

As I have read in another post from Tom Lane that there is no support
for dynamic column names in PL/pgSQL (correct me if I'm wrong) - I tried
to implement my trigger functions in PL/Tcl.

PL/Tcl allows to use dynamic column names, but I could not figure out
how to pass strings to a SQL query in PL/Tcl:

Given the following table:

test=# select * from z;
u | v | w
---+---+---
a | x | y
b | z | z
(2 rows)

and this function:

CREATE OR REPLACE FUNCTION pgtest(VARCHAR) RETURNS VARCHAR AS '
spi_exec "SELECT u from z where v = ''[quote $1]''"
return $u
' LANGUAGE 'pltcl';

I get the following results:

test=# select pgtest('x');
ERROR: Attribute 'x' not found
test=# select pgtest('w');
pgtest
--------
b
(1 row)

This indicates that Postgres uses the parameter as column name.
I tried some ways of quoting the parameter, but it is always used
as column name.
How do I pass the value so that it is used as a string literal in
the query. (making pgtest('x') return the value 'a')

Thank You in advance,

Hans

I'm not sure I really understood what you want...

Here is perhaps what you need...

CREATE TABLE t1
(
col1 text
);

create or replace function foo(text) returns text as '
DECLARE
colname ALIAS FOR $1;
sqlquery text;
result text;
BEGIN
sqlquery := ''INSERT INTO t1 (col1 ) SELECT '' || colname || '' from
toto'';
EXECUTE( sqlquery );

SELECT INTO result col1 FROM t1;
DELETE FROM t1;
RETURN result;
END;
' language 'plpgsql';

----------------------------------------------------------------------------
---------------
Patrick Fiche
email : patrick.fiche@aqsacom.com
t�l : 01 69 29 36 18
----------------------------------------------------------------------------
---------------

-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org]On Behalf Of Johann Uhrmann
Sent: Monday, January 27, 2003 4:02 PM
To: pgsql-general@postgresql.org
Subject: [GENERAL] Getting results from a dynamic query in PL/pgSQL

Hello,

is there a possibility to retrieve results from a dynamically generated
query in PL/pgSQL?

That would be like this:

create function foo(text) returns text as '
DECLARE
colname ALIAS FOR $1;
result text;
BEGIN
SELECT INTO result colname from my_table;
RETURN result;
END;
' language 'plpgsql';

The actual column that is to be read from my_table should be passed as
argument to the function.
The example does not read the variable colname but tries to read a
column named "colname" from my_table which is not how it should work.

The keyword "EXECUTE" which could execute dynamic queries cannot return any
value that a select statement would. (At least there is nothing about that
in the docs.)

In order to write a trigger function that reads column names out of a table
and uses those column names afterwards, I need such a functionality.

I tried a workaround by using EXECUTE to create a function that reads
only the columns I need and then calling this dynamically generated
function.
However, that works only one time - then I get the following message:

ERROR: plpgsql: cache lookup for proc 52118 failed

plpgsql seems to cache the dynamically generated function even after it gets
dropped or overwritten with "create or replace function...".

Does anyone know how to use column names stored in variables within
PL/pgSQL?

Thank You in advance,

Johann Uhrmann

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Patrick Fiche wrote:

I'm not sure I really understood what you want...

Here is perhaps what you need...

CREATE TABLE t1
(
col1 text
);

create or replace function foo(text) returns text as '
DECLARE
colname ALIAS FOR $1;
sqlquery text;
result text;
BEGIN
sqlquery := ''INSERT INTO t1 (col1 ) SELECT '' || colname || '' from
toto'';
EXECUTE( sqlquery );

SELECT INTO result col1 FROM t1;
DELETE FROM t1;
RETURN result;
END;
' language 'plpgsql';

Thank You Patrick. I consider Your solution as a workaround as it
uses a temporary table.

As far as I know, PL/Tcl directly supports dynamic table names - but
now I have difficulties to specify a literal value which should not
be treated as column name but as varchar-value.

Please see my other post for details.

Regards,

Hans