sql - How to return temp table result in postgresql function

Question

I am using a temporary table in a function to save some results however I don't know how to return the table from the function. Ideally I would like to do everything in one query (i.e. not two queries: one for calling the function, the other to get data from the temp table).

Currently my main_function() is as follows:

CREATE OR REPLACE FUNCTION main_function() RETURNS void AS
$BODY$
BEGIN

    DROP TABLE IF EXISTS temp_t CASCADE;
    CREATE TEMP TABLE temp_t AS SELECT * FROM tbl_t limit 0;

    EXECUTE 'INSERT INTO temp_t ' || 'SELECT * FROM tbl_t limit 10';

END;
$BODY$
LANGUAGE 'plpgsql' ;

And I am calling it like so:

SELECT * from main_function();
SELECT * from temp_t;

Again, the problem is that I don't actually want to call the second query. The first query should return the temp table as a result, however I cannot do this since the temp table is created in main_function() so it cannot be its return type.

Any ideas on how to achieve this?

Thanks

Answer 1

Inside your main_function():

RETURN QUERY SELECT * FROM temp_t;

...if temp_t table consists of e.g. column1 (type integer), column2 (boolean) and column3 (varchar(100)), you should also define returned type as:

CREATE OR REPLACE FUNCTION main_function(column1 OUT integer, column2 OUT boolean, column3 OUT varchar(100)) RETURNS SETOF record AS
(...)

Another way is to define new data type:

CREATE TYPE temp_t_type AS (
    column1 integer,
    column2 boolean,
    column3 varchar(100)
);

That type can be returned by your functions in the same way as normal data types:

CREATE OR REPLACE FUNCTION main_function() RETURNS SETOF temp_t_type AS
(...)

...and return result from the function in the same way as mentioned above.

Answer 2

Are you sure you need a temporary table? Most of the time, there is a cheaper solution. Your example can simply be:

CREATE OR REPLACE FUNCTION main_function()
  RETURNS SETOF tbl_t AS
$BODY$
BEGIN

RETURN QUERY EXECUTE 'SELECT * FROM tbl_t LIMIT 10';

END
$BODY$
LANGUAGE plpgsql;

You also don't need EXECUTE or even plpgsql for the simple case:

CREATE OR REPLACE FUNCTION main_function()
  RETURNS SETOF tbl_t AS
$BODY$

SELECT * FROM tbl_t LIMIT 10;

$BODY$
LANGUAGE sql;

Never quote the language name. It's an identifier.

Answer 3

instead of

CREATE OR REPLACE FUNCTION main_function() RETURNS void AS

use some like CREATE OR REPLACE FUNCTION main_function() RETURNS TABLE(f1 int, f2 text) AS...