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Possible Duplicate:
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
我必须得到输出(下一步(按a排序)重复记录应该从结果集中排除):
a b
----------- -----------
1 30
2 50
3 50 -- should be excluded
4 50 -- should be excluded
5 60