CREATE TABLE AS is not allowed in a non-volatile function in Postgresql - postgresql

Question

I have wrote this method on postgresql 10 :
create or replace function get_users()
returns TABLE(user_idd uuid, device_idd text, shapee text , datee timestamp) AS
$$
begin
create temp table lines as
SELECT DISTINCT user_id, device_id from olocations;
select uuid_generate_v4(),
o1.user_id,
o1.device_id,
st_astext(ST_Collect(o1.shape)),
date(o1.creation_date_time) as date
from olocations o1
inner join lines on o1. device_id = lines.device_id and o1.user_id = lines.user_id
where o1.user_id = 'd0edfc59-9923-44c3-9c34-ef5aad3cb810'
and o1.device_id = '89984320001811791540'
group by o1.user_id, o1.device_id, date
order by date ASC ;
DROP TABLE lines;
end
$$
LANGUAGE 'plpgsql'
IMMUTABLE
SECURITY DEFINER
COST 100;
After create method without any problem, when i call my method:
select * from get_users();
I got this error:
sql> select from get_users()
[2018-09-30 17:23:23] [0A000] ERROR: CREATE TABLE AS is not allowed in a non-volatile function
[2018-09-30 17:23:23] Where: SQL statement "create temp table lines as
[2018-09-30 17:23:23] SELECT DISTINCT user_id, device_id from olocations"
[2018-09-30 17:23:23] PL/pgSQL function get_users() line 3 at SQL statement
I think i can not create table in method? right?

Answer 1

The function cannot be IMMUTABLE, define it as VOLATILE.
Per the documentation:
Any function with side-effects must be labeled VOLATILE, so that calls to it cannot be optimized away.
In this case this side-effect is the table creation.
Update.
Use return query to return rows generated by the query:
...
return query
select uuid_generate_v4(),
o1.user_id,
o1.device_id,
st_astext(ST_Collect(o1.shape)),
date(o1.creation_date_time) as date
...