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Alex Rivera
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In the following query SELECT col1,col2 FROM table1 WHERE col3='value1' AND col4='value2' If I have 2 separate indexes one on col3 and the other on col4 , Which one of them will be used in this query ? I read somewhere that for each table in the query only one index is used. Does that mean that there is no way for the query to use both indexes ? Secondly, If I created a composite index using both col3 and col4 together but used only col3 in the WHERE clause will that be worse for the performance? example: SELECT col1,col2 FROM table1 WHERE col3='value1' Lastly, Is it better to just use Covering indexes in all cases ? and does it differ between MYISAM and innodb storage engines ?
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