Re: A fine point about OUTER JOIN semantics

Поиск
Список
Период
Сортировка
От Thomas Lockhart
Тема Re: A fine point about OUTER JOIN semantics
Дата
Msg-id 39B09C2A.FEBC6B85@alumni.caltech.edu
обсуждение исходный текст
Ответ на A fine point about OUTER JOIN semantics  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: A fine point about OUTER JOIN semantics
Список pgsql-hackers
> Am I right in thinking that the WHERE clause of a query must logically
> be applied *after* any joins specified in the FROM clause?
...
> This shows that JOIN/ON conditions for outer joins are not semantically
> interchangeable with WHERE conditions.

Right. In some cases, an outer join with WHERE restrictions reduces to
an inner join (so the qualification clauses can be consolidated). Our
optimizer should be on the lookout for that, at least eventually.
                     - Thomas


В списке pgsql-hackers по дате отправления:

Предыдущее
От: Tom Lane
Дата:
Сообщение: Re: Backend-internal SPI operations
Следующее
От: Thomas Lockhart
Дата:
Сообщение: (Slightly) broken makefiles