# where is the performance hit with null values in indexes?

**URL:** <https://forums.percona.com/t/where-is-the-performance-hit-with-null-values-in-indexes/1422>\
**Category:** Other MySQL® Questions\
**Created:** [June 2, 2010, 4:19am UTC](https://forums.percona.com/t/where-is-the-performance-hit-with-null-values-in-indexes/1422 "2010-06-02T04:19:14Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![billybob](https://avatars.discourse-cdn.com/v4/letter/b/e79b87/32.png) [@billybob](https://forums.percona.com/u/billybob)\
**Post date:** [June 2, 2010, 4:19am UTC](https://forums.percona.com/t/where-is-the-performance-hit-with-null-values-in-indexes/1422/1 "2010-06-02T04:19:14Z")

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Hi

Where is the performance hit with having NULL values in indexes. On the creation of the record index, on retrieval, or both ?

Cheers

Billy.

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**Author:** ![xaprb](https://avatars.discourse-cdn.com/v4/letter/x/49beb7/32.png) [@xaprb](https://forums.percona.com/u/xaprb)\
**Post date:** [June 7, 2010, 6:05am UTC](https://forums.percona.com/t/where-is-the-performance-hit-with-null-values-in-indexes/1422/2 "2010-06-07T06:05:51Z")

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I can’t think of a case where there would be a problem on insert. For retrieval, it depends on the query. Have you read High Performance MySQL Second Edition? We talked about it at length there.