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                            業務里, 要把一批數據導入現在使用的表里, 導入后有很多重復的, 要根據某個唯一字段去重(非主鍵),如果同一條數據有很多條相同, 需要多次執行
大的id是后導入的, 之前的保留, SQL代碼是, 先group和MAX, HAVING  分組并把有2條及以上重復數據的找到最大的字段,找到后進行刪除, 由于同一張表, 不能直接 delete的時候直接in同一張表（會報錯 xxx for update in FROM clause 等錯誤）, 需要中間轉一道。

```
DELETE 
FROM
	表
WHERE
	id IN ( 
            SELECT a.id FROM ( 
                SELECT MAX( id ) id FROM 表 GROUP BY 字段 HAVING COUNT( 字段)> 1 
        ) a );
```


                    
                
        
                
            
        
                
    
                
    
                
        
                
    
                

                







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