Re: UPDATE using query; per-row function calling problem
От | Rory Campbell-Lange |
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Тема | Re: UPDATE using query; per-row function calling problem |
Дата | |
Msg-id | 20110905205501.GA13235@campbell-lange.net обсуждение исходный текст |
Ответ на | Re: UPDATE using query; per-row function calling problem (David Johnston <polobo@yahoo.com>) |
Ответы |
Re: UPDATE using query; per-row function calling problem
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Список | pgsql-general |
On 02/09/11, David Johnston (polobo@yahoo.com) wrote: > > In my "-1" example, am I right in assuming that I created a correlated > > subquery rather than an correlated one? I'm confused about the > > difference. > > > Correlated: has a where clause that references the outer query > Un-correlated: not correlated > > Because of the where clause a correlated sub-query will return a > different record for each row whereas an un-correlated sub-query will > return the same record for all rows since the where clause (if any) is > constant. Hi David -- thanks for the clarification. However I'm still a little confused. As I understand it the following is a un-correlated sub-query: UPDATE slots SET a = 'a' ,b = (SELECT uuid_generate_v1()) WHERE c = TRUE; and the following, without a 'WHERE', is a correlated sub-query: UPDATE slots SET a = 'a' ,b = uuid_generate_v1() WHERE c = TRUE; Is the point that the lower is not a sub-query at all? Regards Rory
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