Peter Eisentraut wrote:
> > =# select n from (values ('été' collate "myfr"), ('ete')) x(n)
> > group by 1 order by 1 ;
> > n
> > -----
> > ete
> > (1 row)
> >
> > =# select n from (values ('été' collate "myfr"), ('ete')) x(n)
> > group by 1 order by 1 desc;
> > n
> > -----
> > été
> > (1 row)
>
> I don't see anything wrong here. The collation says that both values
> are equal, so which one is returned is implementation-dependent.
Is it, but it's impractical if the product of seemingly the same GROUP BY
flip-flops between its different valid results. If it can't be avoided, then
okay. If it can be avoided at little cost, then it would be better to do it.
As a different example, the regression tests are somewhat counting on
this already. Consider this part:
+CREATE TABLE test3ci (x text COLLATE case_insensitive);
+INSERT INTO test1ci VALUES ('abc'), ('def'), ('ghi');
+INSERT INTO test2ci VALUES ('ABC'), ('ghi');
+INSERT INTO test3ci VALUES ('abc'), ('ABC'), ('def'), ('ghi');
...
+SELECT x, count(*) FROM test3ci GROUP BY x ORDER BY x;
+ x | count
+-----+-------
+ abc | 2
+ def | 1
+ ghi | 1
+(3 rows)
If ABC was returned here instead of abc for whatever reason,
that would be correct strictly speaking, yet "make check" would fail.
That's impractical.
Best regards,
--
Daniel Vérité
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