在ORACLE SQL中删除半重复行

Question

我的表中有行需要根据几列重复进行删除。

e.g Col1中，col2的，COL3，COL4

如果Col1中，col2的和COL3是重复的，无论是在什么COL4价值我想这两个副本删除。我该怎么做呢？

Answer 1

您可以使用where条款做到这一点：通过这些ID

delete from t 
    where (col1, col2, col3) in (select col1, col2, col3 
           from t 
           group by col1, col2, col3 
           having count(*) > 1 
           ); 

Answer 2

集团与具有是否有重复检查。用这样找到的重复项删除记录。

delete from mytable 
where (col1,col2,col3) in 
(
    select col1,col2,col3 
    from mytable 
    group by col1,col2,col3 
    having count(*) > 1 
); 

Answer 3

使用EXISTS到如果与相同COL1，COL2和COL3另一行以较低的COL4值存在删除行。即保留一个col1，col2，col3行。

delete from tablename t1 
where exists (select 1 from tablename t2 
       where t2.col1 = t1.col1 
       and t2.col2 = t1.col2 
       and t2.col3 = t1.col3 
       and t2.col4 < t1.col4) 

同时删除/所有的行，跳过COL4条件，做一个group by代替：

delete from tablename t1 
where exists (select 1 from tablename t2 
       where t2.col1 = t1.col1 
       and t2.col2 = t1.col2 
       and t2.col3 = t1.col3 
       group by t2.col1, t2.col2, t2.col3 
       having count(*) > 1)