| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> |
| Cc: | Don Baccus <dhogaza(at)pacifier(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: PG 7.2b4 bug? |
| Date: | 2001-12-17 21:13:08 |
| Message-ID: | 7062.1008623588@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> writes:
> However, I'd think:
> "select (select nextval from test_seq) from multiple_rows;"
> should give you different values and doesn't, although
> "select (select nextval from test_seq where i IS NULL or i IS NOT NULL)
> from multiple_rows;" does give you different values.
In the first case, the subselect is visibly not dependent on the outer
query, so it's evaluated only once; in the second case it has to be
re-evaluated for each row using that row's value of i. You can see the
difference (InitPlan vs. SubPlan) in the query's EXPLAIN output.
regards, tom lane
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