Record returned from function has columns concatenated

Question

I have a table which stores account changes over time. I need to join that up with two other tables to create some records for a particular day, if those records don\'t alre

Answer 1

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

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

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As for the query:

Postgres 9.3+

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 1
   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

The short notations 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 avoid 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 1
       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 we better decompose in the outer query:

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

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Postgres 10 finally re-implemented set-returning functions in the SELECT list to fix unexpected side effects.

Answer 2

Use the function in the from clause

Select
    '2014-08-12' As day,
    0 As inbytes,
    0 As outbytes,
    acct.username,
    acct.accountid,
    acct.userid,
    asfd.*
From
    account_tab acct
    cross join lateral
    account_servicetier_for_day(acct.accountid, '2014-08-12') asfd
Where acct.isdsl = 1
    And acct.dslservicetypeid Is Not Null
    And acct.accountid Not In (Select accountid From dailyaccounting_tab Where Day = '2014-08-12')
Order By acct.username