[prev in list] [next in list] [prev in thread] [next in thread] 

List:       pgsql-bugs
Subject:    Re: BUG #15551: Date/Time comparison not correct when the comparison is inside join clause and invol
From:       Andrew Gierth <andrew () tao11 ! riddles ! org ! uk>
Date:       2018-12-14 11:32:31
Message-ID: 87o99oz6w8.fsf () news-spur ! riddles ! org ! uk
[Download RAW message or body]

>>>>> "PG" == PG Bug reporting form <noreply@postgresql.org> writes:

 PG> Note: the fourth quarter (*-12-31) of all years are missing.

So the problem here is that you're trying to identify quarters by the
_last_ date, not by the _first_ date.

If you add 3 months to Sept 30th, you get Dec 30th, NOT Dec 31st.
It so happens that adding 3 months to Mar 31st gives Jun 30th, and
adding 3 months to Jun 30th gives Sep 30th, and adding 3 months to
Dec 31st gives Mar 31st, so it's only the one case that fails here.

But if you identify the quarter by its _first_ date, you have no
problem.

date_trunc('quarter', somedate::timestamp) can help with this, but
remember to cast the date to timestamp (without time zone) in the call,
otherwise you'll get incorrect results due to timezone issues.

 PG> The only difference among these query lies in the join clause
 PG> involving date / time comparison having date / time operators being
 PG> used:

 PG> 1st: ct1."time" = ct2."time" + interval '3 months'
 PG> 2nd: ct2."time" = ct1."time" - interval '3 months'
 PG> 3rd: ct1."time" = ct2."time" + interval '3 months' or ct2."time" =
 PG> ct1."time" - interval '3 months'

 PG> It seems to me all the 3 conditions are logically same and should
 PG> have the same result.

Well, in the presence of months of variable lengths, they clearly are
not equivalent and cannot be. So no bug here.

-- 
Andrew (irc:RhodiumToad)

[prev in list] [next in list] [prev in thread] [next in thread]