Access data of variable in PL/PgSQL - postgresql

Question

I have a PL/PgSQL function like this:
CREATE FUNCTION get_value(firstval integer) RETURNS SETOF mytable AS
$func$
DECLARE
current mytable;
BEGIN
SELECT fv FROM mytable WHERE fv = fistval INTO current;
IF current IS NULL THEN
INSERT INTO mytable(fv) VALUES (firstval);
END IF;
RETURN current.fv;
END
$func$ LANGUAGE plpgsql;
I need to return a specific row (fv) of the current variable, but this code is not working (it does not return anything), so how I have to do this?

Answer 1

There are lot of issues:
current is declared like record. But you try to assign integer value to this composite variable SELECT INTO.
The return from table functions should be realised by RETURN TABLE statement. There are not any table with name mytable. In Postgres concept - RETURNS SETOF mytable means - returns rows of type like table "mytable".
The test IS NULL is not safe in this case. You want to check FOUND variable.
Maybe you don't want to return table - then there is badly used SETOF clause.
CREATE OR REPLACE FUNCTION get_value(firstval int)
RETURNS mytable AS $$
DECLARE
_r mytable;
BEGIN
SELECT * FROM mytable WHERE fv = firstval INTO _r;
IF NOT FOUND THEN
INSERT INTO mytable(fv) VALUES(firstval);
SELECT * FROM mytable WHERE fv = firstval INTO _r;
END IF;
RETURN _r;
END;
$$ LANGUAGE plpgsql;
Attention! - this code maybe does what you want, but it is not safe against race conditions. Better to use Postgres statement INSERT ON CONFLICT DO.
Please, try to read documentation first - it is designed differently than you are expecting.