On 12/15/06, Tom Lane <[EMAIL PROTECTED]> wrote:
"Aaron Bono" <[EMAIL PROTECTED]> 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
So if I don't want the duplicated WITHIN the two queries to be eliminated, I
use UNION ALL?
Thanks!
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Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com
http://codeelixir.com
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