Re: INNER JOINS in sql-select.html
От | Tom Lane |
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Тема | Re: INNER JOINS in sql-select.html |
Дата | |
Msg-id | 3687.1067554564@sss.pgh.pa.us обсуждение исходный текст |
Ответ на | INNER JOINS in sql-select.html (Stefan Weiss <spaceman-4b9f8-20030703@ausgehaucht.sensenmann.at>) |
Ответы |
Re: INNER JOINS in sql-select.html
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Список | pgsql-docs |
Stefan Weiss <spaceman-4b9f8-20030703@ausgehaucht.sensenmann.at> writes: > From <doc/html/sql-select.html>: > | A CROSS JOIN or INNER JOIN is a simple Cartesian product, the same > | as you get from listing the two items at the top level of FROM. CROSS > | JOIN is equivalent to INNER JOIN ON (TRUE), that is, no rows are > | removed by qualification. > I thought that by using the second form, you would be able to do > 'explicit' joins, effectivly telling the planner in which order to > join multiple tables (in case you have to join 10+ tables)? They are semantically equivalent, but not necessarily the same from a performance point of view. The potential performance issues are covered elsewhere; I think it would just obfuscate matters to try to include that topic here. regards, tom lane
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