我的指数结构如下:
BTREE merchant_id
BTREE flag
BTREE test (merchant_id, flag)
I do a SlectT query as a :
SELECT badge_id, merchant_id, badge_title, badge_class
FROM badges WHERE merchant_id = 1 AND flag = 1
what index would be better? Does it matter if they are in a seperate index?
回答诸如“Which列”和“使用某种指数进行质问吗?”等问题,你可以使用EXPLAIN>/code>,。 见优良条款。 用<条码>EXPLAIN分析速成表,全面概述在优化查询和图表时使用<条码>EXPLAIN的情况。
一般来说,如果能够把几个栏中的一栏索引成指数,那么,有益的总则是将所有记录中“最独特”或“最有选择”一栏索引;也就是说,将各行各有最多不同数值的一栏索引。 我猜测,就你而言,merchant_id。 第1栏载有大多数独特的数值,因此可能应当加以指数化。 您可以核实,指数选择最好使用EXPLAIN。
请注意,“指数是最有选择的一栏”的规则不一定适用于混合指数第一栏(也称为化合物或多栏)的选择。 这取决于您的询问。 例如,如果employee_id 是最具选择性的一栏,但你需要填写诸如SlectT* 等查询,这些询问来自WHERE旗=17,然后作为表badges的唯一索引,综合索引<代码>(employee_id,code),意味着查询结果将载于完整的表格扫描。
在3个指数中,你没有真正需要一个单独的商家资格指数,因为商家佣可使用你的“测试”指数。
More details: http://dev.mysql.com/doc/refman/5.0/en/multiple-column-indexes.html
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