Re: Unions and Grouping

"Aaron Bono" <postgresql(at)aranya(dot)com> writes:
> My question, what do the SQL Specifications say should happen on a Union?
> Is it supposed to eliminate duplicates even WITHIN the individual queries
> that are being unioned?

Yes. SQL92 7.10 saith:

b) If a set operator is specified, then the result of applying
the set operator is a table containing the following rows:

i) Let R be a row that is a duplicate of some row in T1 or of
some row in T2 or both. Let m be the number of duplicates
of R in T1 and let n be the number of duplicates of R in
T2, where m >= 0 and n >= 0.

ii) If ALL is not specified, then

Case:

1) If UNION is specified, then

Case:

A) If m > 0 or n > 0, then T contains exactly one dupli-
cate of R.

B) Otherwise, T contains no duplicate of R.

regards, tom lane