| From: | shili <shi_li_1992(at)163(dot)com> |
|---|---|
| To: | pgsql-general(at)postgresql(dot)org |
| Subject: | how to import "where exists（subquery）" EXISTS CONDITION performance? |
| Date: | 2015-12-02 07:51:23 |
| Message-ID: | 1449042683403-5875801.post@n5.nabble.com |
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| Thread: | |
| Lists: | pgsql-general |
I had saw this sentence: SQL statements that use the EXISTS condition in
PostgreSQL are very inefficient since the sub-query is RE-RUN for EVERY row
in the outer query's table. There are more efficient ways to write most
queries, that do not use the EXISTS condition. So,I want to know how
PostgreSQL to implement the EXISTS condition? Is that sentence true? and,if
that is true,are there any methods to import the performance of the EXISTS
condition?
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