Hi,



> What's the expected result if the tuple from subselect is more than 1?

Error, per SQL99 section 7.14:

         1) If the cardinality of a <row subquery> is greater than 1
(one),
            then an exception condition is raised: cardinality violation.

I expect no update at all in case of void result set, is this the case ?

No, you get nulls; it's a subquery not a join.  Per SQL99 7.1:

            c) If the <row value constructor> is a <row subquery>, then:

              i) Let R be the result of the <row subquery> and let D be
the
                 degree of R.

             ii) If the cardinality of R is 0 (zero), then the result of
the
                 <row value constructor> is D null values.

            iii) If the cardinality of R is 1 (one), then the result of
the
                 <row value constructor> is R.

                        regards, tom lane


To allow both of the above to hold, I think the subselect will have to be
treated like a EXPR_SUBLINK subquery. I was wondering if we have a similar
mechanism for plain selects/subselects to check and restrict their output to
a single row.

Regards,
Nikhils
--
EnterpriseDB               http://www.enterprisedb.com

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