SQL:đếm số giá trị riêng biệt trong mỗi cột

hãy thử cái này (cú pháp sql server 2005):

DECLARE @YourTable table (col1  varchar(5)
                         ,col2  int
                         ,col3  datetime
                         ,col4  char(3)
                         )

insert into @YourTable values ('abcdf',123,'1/1/2009','aaa')
insert into @YourTable values ('aaaaa',456,'1/2/2009','bbb')
insert into @YourTable values ('bbbbb',789,'1/3/2009','aaa')
insert into @YourTable values ('ccccc',789,'1/4/2009','bbb')
insert into @YourTable values ('aaaaa',789,'1/5/2009','aaa')
insert into @YourTable values ('abcdf',789,'1/6/2009','aaa')


;with RankedYourTable AS
(
SELECT
    ROW_NUMBER() OVER(PARTITION by col1 order by col1) AS col1Rank
        ,ROW_NUMBER() OVER(PARTITION by col2 order by col2) AS col2Rank
        ,ROW_NUMBER() OVER(PARTITION by col3 order by col3) AS col3Rank
        ,ROW_NUMBER() OVER(PARTITION by col4 order by col4) AS col4Rank
    FROM @YourTable
)
SELECT
    SUM(CASE WHEN      col1Rank=1 THEN 1 ELSE 0 END) AS col1DistinctCount
        ,SUM(CASE WHEN col2Rank=1 THEN 1 ELSE 0 END) AS col2DistinctCount
        ,SUM(CASE WHEN col3Rank=1 THEN 1 ELSE 0 END) AS col3DistinctCount
        ,SUM(CASE WHEN col4Rank=1 THEN 1 ELSE 0 END) AS col4DistinctCount
    FROM RankedYourTable

ĐẦU RA:

col1DistinctCount col2DistinctCount col3DistinctCount col4DistinctCount
----------------- ----------------- ----------------- -----------------
4                 3                 6                 2

(1 row(s) affected)