重复删除

Question

可能重复：
Delete duplicate records from a SQL table without a primary key

我有数据：

SELECT 
      a 
     , b 
    FROM 
    (
     select a = 1, b = 30 
     union all 
     select a = 2, b = 50 
     union all 
     select a = 3, b = 50 
     union all 
     select a = 4, b = 50 
     union all 
     select a = 5, b = 60 
    ) t 

我有一个）dublicate记录，以获取输出（下一个（顺序应从结果集中排除）：

a   b 
----------- ----------- 
1   30 
2   50 
3   50 -- should be excluded 
4   50 -- should be excluded 
5   60 

Answer 1

SELECT 
      min(a) as a 
     , b 
    FROM 
    (
     select a = 1, b = 30 
     union all 
     select a = 2, b = 50 
     union all 
     select a = 3, b = 50 
     union all 
     select a = 4, b = 50 
     union all 
     select a = 5, b = 60 
    ) t 
GROUP BY b  
ORDER BY a 

Answer 2

在oracle中我能够做到这一点使用GROUP BY子句，你应该能够做到类似。

select min(a), b 
from (select 1 a, 30 b 
     from dual 
     union all 
     select 2 a, 50 b 
     from dual 
     union all 
     select 3 a, 50 b 
     from dual 
     union all 
     select 4 a, 50 b 
     from dual 
     union all 
     select 5 a, 60 b from dual) 
group by b; 

编辑：看起来像其他人想出了一个MS SQL的解决方案，我会在这里虽然离开这个给后人。

Answer 3

做到这一点，最简单的方法是用一个简单的GROUP BY：

SELECT 
     a 
    , b 
INTO #tmp 
FROM 

(
    select a = 1, b = 30 
    union all 
    select a = 2, b = 50 
    union all 
    select a = 3, b = 50 
    union all 
    select a = 4, b = 50 
    union all 
    select a = 5, b = 60 
) t 


SELECT DISTINCT MIN(a) AS a,b 
FROM #tmp 
GROUP BY b 
ORDER BY a