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Re: Use of SUBSTR with an index
Posted by: Andrew Gilfrin
Date: July 22, 2005 07:48AM

Not sure about MySQL but in Oracle the optimiser will make a decision based on how many rows are likely to be returned from the select. If it's greater than around 20% of all the rows in the table it generally doesn't use the index.

There is an overhead in using indexes and in some cases it's slower using an index against a simple scan of the table.

Andrew Gilfrin
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Re: Use of SUBSTR with an index
July 22, 2005 07:48AM


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