Postgresql9-4 - User define function that uses a join - ERROR: missing FROM-clause entry for table - plpgsql

Question

I am venturing into pg/sql for the first time and I wrote this function that (attempts) to return results from a query that uses a JOIN.
The query works when I run on it self. However, when it is running within the function I wrote it complains about a missing "FROM". I also used table aliases hoping that it may fix the problem but it did not.
I am getting information from the following tables and rows.
TABLE | ROW
---------------------------------------
banned_users | banned_lcl_account
---------------------------------------
rhost_active_users | active_users
Here is the error when I run my function
ERROR: missing FROM-clause entry for table "a_u"
LINE 1: SELECT LOOP_V.a_u.ipaddress
And here is the function I wrote.
CREATE OR REPLACE FUNCTION GET_BANNED_ACTIVE_USERS()
RETURNS TABLE
(
SRC_HOST TEXT,
DST_HOST TEXT
)
AS $$
DECLARE
LOOP_V RECORD;
BEGIN
FOR LOOP_V IN (
select
b_u.banned_lcl_account,
a_u.ipaddress,
a_u.hostip,
date_trunc ('second', a_u.time_captured)
from banned_users as b_u
inner join rhost_active_users as a_u
on b_u.banned_lcl_account = a_u.active_users
and a_u.hostip <> 'TTY Login'
or a_u.hostip <> 'Local PTS Login'
)
LOOP
SRC_HOST := LOOP_V.a_u.ipaddress;
DST_HOST := LOOP_V.a_u.hostip;
END LOOP;
END; $$
LANGUAGE 'plpgsql';
--select CHECK_BANNED_ACCOUNTS()

Answer 1

your problem is this:
SRC_HOST := LOOP_V.a_u.ipaddress;
DST_HOST := LOOP_V.a_u.hostip;
The record that is used for the loop variable only contains column names, not their table aliases. So the record only has the fields: ipaddress and hostip. So your immediate problem can be fixed using:
SRC_HOST := LOOP_V.ipaddress;
DST_HOST := LOOP_V.hostip;
However the whole function is overly complex. You don't need the loop nor do you need PL/pgSQL. This can be written as a simple SQL function:
CREATE OR REPLACE FUNCTION GET_BANNED_ACTIVE_USERS()
RETURNS TABLE (SRC_HOST TEXT,DST_HOST TEXT)
AS $$
select a_u.ipaddress,
a_u.hostip,
from banned_users as b_u
join rhost_active_users as a_u
on b_u.banned_lcl_account = a_u.active_users
and (a_u.hostip <> 'TTY Login' or a_u.hostip <> 'Local PTS Login')
$$
LANGUAGE sql;
Note that I also removed the unused columns from the SELECT statement in order to match the function's signature of returning two columns
Some additional notes:
--select CHECK_BANNED_ACCOUNTS()
This is wrong, you need to use a set returning function like a table:
select *
from CHECK_BANNED_ACCOUNTS();
And finally:
LANGUAGE 'plpgsql';
The language name is an identifier, do not enclose it in single quotes:
LANGUAGE plpgsql;
or
LANGUAGE sql;