Re: Unions and Grouping - Mailing list pgsql-sql

"Aaron Bono" <postgresql@aranya.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