On 12/1/2015 11:51 PM, shili wrote:
> 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?
that would depend on the specific query with which you're having
performance problems.
start with EXPLAIN ANALYZE SELECT ....restofyourquery....; to see
whats going on
--
john r pierce, recycling bits in santa cruz