| From: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> |
|---|---|
| To: | Alex <alex(at)meerkatsoft(dot)com> |
| Cc: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Unique Index |
| Date: | 2005-01-19 15:19:59 |
| Message-ID: | 20050119071649.H54178@megazone.bigpanda.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-general |
On Thu, 20 Jan 2005, Alex wrote:
> i have a unique index on a table over multiple columns. If now one of
> the records has a null value in one of the indexed columns i can insert
> the same record multiple times.
>
> Is this a problem within postgres or expected?
Expected. NULLs are effectively not considered as the same for the
purposes of UNIQUE.
The predicate basically functions as:
2) If there are no two rows in T such that the value of each column
in one row is non-null and is equal to the value of the cor-
responding column in the other row according to Subclause 8.2,
"<comparison predicate>", then the result of the <unique predi-
cate> is true; otherwise, the result of the <unique predicate>
is false.
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