Postgres function with list argument and in clause - sql

Question

How to create a function which takes as argument integer[] parameter and executing query with IN clause with this parameter in loop.
In loop I want execute next select and result of this query I would like return.
Something like that:
CREATE OR REPLACE FUNCTION function_which_i_want(my_argument integer[]) RETURNS my_schema_and_table[] AS
$BODY$
DECLARE
result my_schema_and_table[];
BEGIN
FOR l IN SELECT * FROM table2 WHERE id in (my_argument) LOOP
SELECT * FROM my_schema_and_table;
END LOOP;
END;
...
I want to get union of each select in loop. one huge joined result.
Is this possible? Please help.

Answer 1

PL/pgSQL function
It could look like this:
CREATE OR REPLACE FUNCTION func1(_arr integer[])
RETURNS SETOF my_schema_and_table
LANGUAGE plpgsql AS
$func$
DECLARE
l record;
BEGIN
FOR l IN
SELECT *
FROM lookup_table
WHERE some_id = ANY(_arr)
LOOP
RETURN QUERY
SELECT *
FROM my_schema_and_table
WHERE link_id = l.link_id;
END LOOP;
END
$func$;
Assuming you actually want a SET of rows from your my_schema_and_table, not an array? To return the result of SELECT * FROM my_schema_and_table, declare the function as RETURNS SETOF my_schema_and_table
Rewrite the IN construct to = ANY(_arr). That's the way to use an array parameter directly. Logically equivalent.
Or use unnest() and join to the resulting table like #Clodoaldo demonstrates. That can be faster with long arrays.
Simplify to plain SQL function
This simple SQL function does the same:
CREATE OR REPLACE FUNCTION func2(_arr integer[])
RETURNS SETOF my_schema_and_table
LANGUAGE sql AS
$func$
SELECT t.*
FROM (SELECT unnest($1) AS some_id) x
JOIN lookup_table l USING (some_id)
JOIN my_schema_and_table t USING (link_id);
$func$
Assuming both tables have link_id.
Call:
SELECT * FROM func2('{21,31}'::int[]);

Answer 2

CREATE OR REPLACE FUNCTION function_which_i_want(my_argument integer[])
RETURNS my_schema_and_table[] AS
$BODY$
DECLARE
result my_schema_and_table[];
BEGIN
for l in
select t.*
from
table2 t
inner join
unnest(my_argument) m(id) on m.id = t.id
loop
SELECT * FROM my_schema_and_table;
END LOOP;
END;