PostgreSQL stored procedure to return rows or empty set

I have a stored procedure, which RETURNS SETOF ct_custom_type and inside I do

RETURN QUERY EXECUTE 'some dynamic query'

And I want to do this: If this 'dynamic query' returns >= 10 rows, I want to return them, but if it returns only < 10 rows, I don't want to return anything (empty set of ct_custom_type).

I tried:

RETURN QUERY EXECUTE 'some dynamic query'

GET DIAGNOSTICS variable = ROW_COUNT;
IF variable < 10 THEN

    # I don't know what to do here or how to accomplish this

END IF;

If I do RETURN QUERY SELECT 0, 0, ''::text; in the IF block (because ct_custom_type is a composite type of (integer, integer, text), it just adds this 'empty row' to previous query result, but I don't want to return anything in this case, I can do RETURN;, but it will return that previous result and I want to discard it.

I have it like this:

EXECUTE 'dynamic query';

GET DIAGNOSTICS variable = ROW_COUNT;
IF variable >= 10 THEN
    RETURN QUERY EXECUTE 'dynamic query';
END IF;

and it works, but I didn't want to do this query two times.

You can do something along the following lines:

test=> CREATE OR REPLACE FUNCTION temptabl(cnt integer)
RETURNS SETOF integer AS
$body$
BEGIN
    CREATE TEMPORARY TABLE tmp_container ON COMMIT DROP AS
    SELECT a
    FROM generate_series(1, cnt) t(a);

    IF (SELECT count(1) FROM tmp_container) > 5
    THEN
        RETURN QUERY SELECT a FROM tmp_container;
    END IF;
END;
$body$
LANGUAGE plpgsql;

test=> SELECT * FROM temptabl(4);
 temptabl 
----------
(0 rows)

test=> SELECT * FROM temptabl(6);
 temptabl 
----------
        1
        2
        3
        4
        5
        6
(6 rows)

This way you have to perform your original query only once. All other statements work on the temporary table.

StackExchange Database Administrators Q#40214, answer score: 8