Am 12.02.2014 02:23, schrieb Zhigang Zhang: > 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
because ‘%abcd’ can't work in case of a index how do you imagine that? read how a index works technically 'abcd%' may work but '%abcd' is impossible independent what engine, this don't work and won't ever work you may have luck with fulltext search (and it's other drawbacks) https://dev.mysql.com/doc/refman/5.5/en/fulltext-search.html
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