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                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                最近做項目寫sql的時候同時使用到了order by 和 group by.然而查詢出來的結果不是自己想象中的那樣. 下面來分析一樣原因: mysql 寫sql的順序: select -> from-> where->group by->having->order by. 但mysql的解析器執行順序: from-> where->group by->having->select->order by. 所以,從執行的流程來看,是先group by 然后在 order by. order by拿到的結果里已經是group by以后的結果. 因此,order by的字段必須是group by 里面已經存在的字段.
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