mysql - Using an index when searching by two columns -

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i have large table from fetch data. data received using comparison of 2 columns, , b. there should not many rows match a.

i want add index better performance. question need set index on both , b or enough set index on a?

you can refer link better indexing.

http://www.programmerinterview.com/index.php/database-sql/what-is-an-index/


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