From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | pgsql-sql(at)hub(dot)org |
Subject: | Re: [SQL] Re: "order by" weirdness |
Date: | 1999-09-27 13:47:15 |
Message-ID: | 26126.938440035@sss.pgh.pa.us |
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Lists: | pgsql-sql |
>> consider these three statements:
>>
>> create table t (id integer, date datetime ) ;
>> select id from t group by id ;
>> select id from t group by id order by max(date) ;
>>
>> Is it correct behavior that the second select returns
>> one row whereas the first select returns zero rows?
No, it is not. (Although it took a few rounds of discussion in the
mailing lists to get everyone to agree on that... if you check the
archives you will find this issue has come up repeatedly.)
I have in fact just fixed this in current sources. So, in 6.6 and
later, both statements will return zero rows if t is empty.
Note that with aggregates and no GROUP BY, you will get a row:
select count(id) from t ;
count
-----
0
(1 row)
select max(id) from t ;
max
---
(1 row)
which is correct behavior and will not change.
regards, tom lane
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