On Sun, Dec 14, 2003 at 22:17:35 -0500,
Tom Lane [EMAIL PROTECTED] wrote:
Bruno Wolff III [EMAIL PROTECTED] writes:
If the sort used to select the records sorts on both the distinct
expressions and the order by expressions you will get a sensible
deterministic result.
Sensible in what
On Mon, Dec 15, 2003 at 06:14:59 -0600,
Bruno Wolff III [EMAIL PROTECTED] wrote:
Doing things as above is pretty much the same as normal distinct on
for purposes of which rows get selected. Of the possible rows that
might get returned for a specific set of values from the distinct on
Bruno Wolff III [EMAIL PROTECTED] writes:
Specifically the interpretation I think makes sense is that
SELECT DISTINCT ON (a, b, c) * FROM tablename ORDER BY d, e, f
should be treated as equvialent to
SELECT * FROM
(SELECT DISTINCT ON (a, b, c) FROM tablename ORDER BY a, b, c, d, e, f) AS t
Greg Stark [EMAIL PROTECTED] writes:
So, like DISTINCT ON, GROUP BY also insists on the user providing the
ORDER BY clause. I suppose you could argue postgres could implicitly
introduce an extra sort step when the user-provided ORDER BY doesn't
match the GROUP BY or DISTINCT ON clause but it
Tom Lane [EMAIL PROTECTED] writes:
This was discussed before --- see the archives. I believe the
conclusion was that the results would actually be nondeterministic
if we used two sort steps (that's what the code comment means by
rather unpredictable).
Does the non-determinism you're
On Sun, Dec 14, 2003 at 18:09:33 -0500,
Tom Lane [EMAIL PROTECTED] wrote:
This was discussed before --- see the archives. I believe the
conclusion was that the results would actually be nondeterministic
if we used two sort steps (that's what the code comment means by
rather
Neil Conway [EMAIL PROTECTED] writes:
Does the non-determinism you're referring to result from an ORDER BY
on a non-deterministic expression, or the non-determinism that results
from picking an effectively random row because the ORDER BY isn't
sufficient?
The latter --- you don't know which
Bruno Wolff III [EMAIL PROTECTED] writes:
If the sort used to select the records sorts on both the distinct
expressions and the order by expressions you will get a sensible
deterministic result.
Sensible in what sense? ;-)
It seems to me that the existing documentation defines the behavior
On Fri, Dec 12, 2003 at 18:39:20 -0500,
Neil Conway [EMAIL PROTECTED] wrote:
/*
* If the user writes both DISTINCT ON and ORDER BY, then the
* two expression lists must match (until one or the other
* runs out). Otherwise the ORDER
Neil Conway [EMAIL PROTECTED] writes:
We reject the following query:
nconway=# create table abc (a int, b int, c int);
CREATE TABLE
nconway=# select distinct on (a) a, b, c from abc order by b, c, a;
ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY
expressions
What
Greg Stark [EMAIL PROTECTED] writes:
Do you really want:
select distinct on (b,c,a) a,b,c from abc order by b,c,a;
or is that you want
select * from (select distinct on (a) a,b,c order by a) order by
b,c,a;
If I understand you correctly, I don't think I would expect either.
- ORDER BY
We reject the following query:
nconway=# create table abc (a int, b int, c int);
CREATE TABLE
nconway=# select distinct on (a) a, b, c from abc order by b, c, a;
ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY
expressions
This works fine, of course:
nconway=# select distinct
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