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understanding towards Using where; Using temporary; Using filesort is right?
Posted by: ajaz basha
Date: March 23, 2011 08:52AM

Hi all,

I am just new to this forum, so excuse me if question below has already been answered. If so can any one direct me to appropriate link.

Keeping in mind that,

Mysql executes query in single sweep nested loop join method, and Using where means the rows are first extracted by storage engine and then where condition is applied, and temporary is for sorting up the rows.

When explain plan shows the Using where; Using temporary; Using filesort in Extra column in first row for table say X, with rows_column showing 10024 rows.

Does that mean ...

Mysql first reads rows of table X ( i.e. 10024 expected) and
then applies Using where condition on those rows, later
storing matching result ( say 100 rows ) in temporary table and
then sorting these (100 rows) to join with the next table..

So now my question is, have I understood right?
Please correct me if I am wrong..

PS:
The thought came from question does the order in which Using where; Using Temporary; Using filesort matters?
why it cant be in this order in extra column of explain
Using Temporary; Using filesort; Using where ?



Edited 1 time(s). Last edit at 03/23/2011 08:53AM by ajaz basha.

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