count(*)優化

  b_info表50萬條記錄mysql   id爲主鍵    sql cityid和b_classid爲聯合索引緩存   爲防止緩存，關閉查詢緩存對好比下：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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