重复删除 [英] Duplicates removing

问题描述

可能重复：

从没有主键的SQL表中删除重复记录

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

我必须得到输出（next（order by a ）公开记录应从结果集中排除）：

I have to get output (next (order by a) dublicate records should be excluded from result set):

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

推荐答案

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

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