Re: Documentation discrepancy UNIQUE NULLS NOT DISTINCT
| От | David G. Johnston |
|---|---|
| Тема | Re: Documentation discrepancy UNIQUE NULLS NOT DISTINCT |
| Дата | |
| Msg-id | CAKFQuwb5FEcX05QOcnw4M+PNMoYoPLY3Hi5GO5+aDorBVdhN-g@mail.gmail.com обсуждение исходный текст |
| Ответ на | Documentation discrepancy UNIQUE NULLS NOT DISTINCT (Adrian Klaver <adrian.klaver@aklaver.com>) |
| Список | pgsql-general |
On Thu, Jan 19, 2023 at 3:41 PM Adrian Klaver <adrian.klaver@aklaver.com> wrote:
From here:
https://www.postgresql.org/about/featurematrix/detail/392/
UNIQUE NULLS NOT DISTINCT
By default, NULL values are not treated as distinct entries. Specifying
NULLS NOT DISTINCT on unique indexes / constraints will cause NULL
values to be treated distinctly.
From here:
https://www.postgresql.org/docs/current/sql-createindex.html
NULLS DISTINCT
NULLS NOT DISTINCT
Specifies whether for a unique index, null values should be
considered distinct (not equal). The default is that they are distinct,
so that a unique index could contain multiple null values in a column.
and here:
https://www.postgresql.org/docs/current/sql-createtable.html
For the purpose of a unique constraint, null values are not considered
equal, unless NULLS NOT DISTINCT is specified.
I think saying that NULLs are distinct by default is the better way to present this. The documentation disagrees on the verbiage but both state the same truth; the feature matrix page needs to be fixed.
David J.
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