/*已知数据:
Column1 Column2 Column3 Column4
A 10 am 1999-01-01 00:00:00.000
A 11 am 1999-01-02 00:00:00.000
B 12 bm 1999-01-03 00:00:00.000
B 13 bm 1999-01-04 00:00:00.000
C 14 cm 1999-01-05 00:00:00.000
C 15 cm 1999-01-06 00:00:00.000
要求得到数据:
Column1 Column2 Column3 Column4
A 11 am 1999-01-02 00:00:00.000
B 13 bm 1999-01-04 00:00:00.000
C 15 cm 1999-01-06 00:00:00.000 */
--数据装载
Create Table #T(Column1 varchar(10),Column2 int,Column3 varchar(10),Column4 datetime)
insert #T select 'A',10,'am','1999-1-1'
union all select 'A',11,'am','1999-1-2'
union all select 'B',12,'bm','1999-1-3'
union all select 'B',13,'bm','1999-1-4'
union all select 'C',14,'cm','1999-1-5'
union all select 'C',15,'cm','1999-1-6'
--测试语句 方法1：
select a.* from #T a
where (a.Column4) = (select top 1 (Column4) from #T where Column1 = a.Column1 order by Column4 desc)
--测试结果:
Column1 Column2 Column3 Column4
---------- ----------- ---------- ------------------------------------------------------
A 11 am 1999-01-02 00:00:00.000
B 13 bm 1999-01-04 00:00:00.000
C 15 cm 1999-01-06 00:00:00.000
--测试语句 方法2:(最佳效率)
select a.* from #T a join( select Column1,Column4=max(Column4)
from #T group by Column1 ) b on a.Column1=b.Column1 and a.Column4=b.Column4 order by a.Column1
--测试结果 方法2:
Column1 Column2 Column3 Column4
---------- ----------- ---------- ------------------------------------------------------
A 11 am 1999-01-02 00:00:00.000
B 13 bm 1999-01-04 00:00:00.000
C 15 cm 1999-01-06 00:00:00.000
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