Record returned from function has columns concatenated

Generally, to decompose rows returned from a function and get individual columns:

SELECT * FROM account_servicetier_for_day(20424, '2014-08-12');

---

As for the query:

Postgres 9.3 or newer

Cleaner with JOIN LATERAL:

SELECT '2014-08-12' AS day, 0 AS inbytes, 0 AS outbytes
     , a.username, a.accountid, a.userid
     , f.*   -- but avoid duplicate column names!
FROM   account_tab a
     , account_servicetier_for_day(a.accountid, '2014-08-12') f  -- <-- HERE
WHERE  a.isdsl = 1
AND    a.dslservicetypeid IS NOT NULL
AND    NOT EXISTS (
   SELECT FROM dailyaccounting_tab
   WHERE  day = '2014-08-12'
   AND    accountid = a.accountid
   )
ORDER  BY a.username;

The LATERAL keyword is implicit here, functions can always refer earlier FROM items. The manual:

LATERAL can also precede a function-call FROM item, but in this
case it is a noise word, because the function expression can refer to
earlier FROM items in any case.

Related:

• Insert multiple rows in one table based on number in another table

Short notation with a comma in the FROM list is (mostly) equivalent to a CROSS JOIN LATERAL (same as [INNER] JOIN LATERAL ... ON TRUE) and thus removes rows from the result where the function call returns no row. To retain such rows, use LEFT JOIN LATERAL ... ON TRUE:

...
FROM  account_tab a
LEFT  JOIN LATERAL account_servicetier_for_day(a.accountid, '2014-08-12') f ON TRUE
...

Also, don’t use NOT IN (subquery) when you can avoid it. It’s the slowest and most tricky of several ways to do that:

• Select rows which are not present in other table

I suggest NOT EXISTS instead.

Postgres 9.2 or older

You can call a set-returning function in the SELECT list (which is a Postgres extension of standard SQL). For performance reasons, this is best done in a subquery. Decompose the (well-known!) row type in the outer query to avoid repeated evaluation of the function:

SELECT '2014-08-12' AS day, 0 AS inbytes, 0 AS outbytes
     , a.username, a.accountid, a.userid
     , (a.rec).*   -- but be wary of duplicate column names!
FROM  (
   SELECT *, account_servicetier_for_day(a.accountid, '2014-08-12') AS rec
   FROM   account_tab a
   WHERE  a.isdsl = 1
   AND    a.dslservicetypeid Is Not Null
   AND    NOT EXISTS (
       SELECT FROM dailyaccounting_tab
       WHERE  day = '2014-08-12'
       AND    accountid = a.accountid
      )
   ) a
ORDER  BY a.username;

Related answer by Craig Ringer with an explanation, why it’s better not to decompose on the same query level:

• How to avoid multiple function evals with the (func()).* syntax in an SQL query?

Postgres 10 removed some oddities in the behavior of set-returning functions in the SELECT:

• What is the expected behaviour for multiple set-returning functions in SELECT clause?