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:mdesharn...@diffusion.cc] Sent: Wednesday, February 12, 2014 9:41 AM To: Zhigang Zhang; mysql@lists.mysql.com Subject: Re: LIKE sql optimization Sql database doesn't use index in like statement if it starts with % .. like 'abcd%' would work though... 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 <zzgang2...@gmail.com>: For example: Select * from T where col like ‘%abcd’; 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
