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From:kitlenv Date:February 12 2014 1:55am
Subject:Re: LIKE sql optimization
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*read how a index works technically*


On Wed, Feb 12, 2014 at 12:48 PM, Zhigang Zhang <zzgang2008@stripped>wrote:

> I want to know the reason, in my opinion, to scan the smaller index data
> has
> better performance than to scan the whole table data.
>
>
>
>
>
> zhigang
>
>
>
>   _____
>
> From: Mathieu Desharnais [mailto:mdesharnais@stripped]
> Sent: Wednesday, February 12, 2014 9:41 AM
> To: Zhigang Zhang; mysql@stripped
> Subject: Re: LIKE sql optimization
>
>
>
> Sql database doesn't use index in like statement if it starts with % ..
>
>
>
> like 'abcd%' would work though...
>
>
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> To use an index you can store your value using reverse function and index
> it
> .. then your like would use the index.
>
>
>
> 2014-02-11 20:23 GMT-05:00 Zhigang Zhang <zzgang2008@stripped>:
>
> For example:
>
>
>
> Select * from T where col like '%abcd';
>
>
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> The table T is myisam table and we created a index on col.
>
>
>
> As we known, this like sql does not use the index created on col, it
> confuse
> me, why?
>
>
>
> I think in mysiam engine, the index data is smaller, it can use index link
> list to optimize it so as to reduce the disk scan than to the whole table
> scan.
>
>
>
> Thanks.
>
>
>
> Zhigang
>
>
>
>

Thread
LIKE sql optimizationZhigang Zhang12 Feb 2014
  • Re: LIKE sql optimizationReindl Harald12 Feb 2014
  • Re: LIKE sql optimizationMathieu Desharnais12 Feb 2014
    • RE: LIKE sql optimizationZhigang Zhang12 Feb 2014
      • Re: LIKE sql optimizationkitlenv12 Feb 2014
        • Re: LIKE sql optimizationlouis liu12 Feb 2014
          • Re: LIKE sql optimizationMathieu Desharnais12 Feb 2014
      • Re: LIKE sql optimizationReindl Harald12 Feb 2014
        • RE: LIKE sql optimizationZhigang Zhang12 Feb 2014
      • Re: LIKE sql optimizationMorgan Tocker12 Feb 2014
        • RE: LIKE sql optimizationZhigang Zhang12 Feb 2014
        • Re: LIKE sql optimizationJesper Wisborg Krogh12 Feb 2014
          • RE: LIKE sql optimizationZhigang Zhang12 Feb 2014