聯合更新1
update user1 inner join (select user2.usename from user2 join use1 on user1.usename =user2.usename)user2 on user1.usename=user2.usename set user1.over='齊天大圣';語句中括號里的查詢是否多此一舉？
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update user1 inner join (select user2.usename from user2 join use1 on user1.usename =user2.usename)user2 on user1.usename=user2.usename set user1.over='齊天大圣';語句中括號里的查詢是否多此一舉？
2018-06-25
舉報
2018-06-28
可能是數據量太細微了吧 親測兩種的結果都是?
Query OK, 1 row affected (0.00 sec)
2018-06-26
你可以也用where a.user_name=b.user_name來更新，但是你都運行之后會發現按照括號這么寫運行速度比用where條件快0.002ms，這就相當于對sql語句的優化了