使用SQL語句，刪除表中重複的項，保留最小的ID；

在表 tabel 1中，存在大量重複資料，需要刪除重複項，且儲存 ID 為最小的那條記錄。

[SQL] 
delete from table1  WHERE jzmdid in  
( select jzmdid from table1 where yj_month='201805' GROUP BY jzmdid
  HAVING COUNT(jzmdid) >1)  
  and id not in 
( select min(id) as minid
  from table1 where  yj_month='201805' group by jzmdid having count(jzmdid)>1 ) ;

[Err] 1093 - You can't specify target table 'table1' for update in FROM clause
 

[Err] 1093 - You can't specify target table 'table1' for update in FROM clause

分析：Mysql 中Delete和Update 語句，不允許子查詢中出現update和delete要操作表

解決方法：給子查詢外面再加一個查詢

1、刪除重複記錄,儲存 ID最小的一條

-- 1、刪除重複記錄,儲存Id最小的一條
 delete from table1  WHERE yj_month='201805' and jzmdid in  
  ( select * from (
    select jzmdid from table1 where yj_month='201805' GROUP BY jzmdid 
      HAVING COUNT( jzmdid ) >1) s
       ) and id not in 

        ( select minid from (
           select min(id) as minid
            from table1
             where  yj_month='201805' 
              group by jzmdid having count(jzmdid )>1 ) b) ; 

受影響的行: 431250
時間: 106.209s