count(*)优化

  b_info表50万条记录mysql   id为主键    sql cityid和b_classid为联合索引缓存   为防止缓存，关闭查询缓存对好比下：索引 （1）ci   mysql> select sql_no_cache count(*) as num from b_info where  cityid=1 and b_classid=79;it +-------+class | nu

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