自关联去掉组内重复数据

数据库环境：SQL SERVER 2005

　　现有一个表的数据如下，id是主键，p1，p2是字符串类型，如果当前行的p1，p2字段的值分别等于其它行

的字段p2，p1的值，则视这2行记录为一组。比如，id=1和id=5就属于同一组数据。同一组数据只显示id最小

的那行记录，没有组的数据全部显示。

WITH    c1
AS ( SELECT   1 AS id ,
'A' AS p1 ,
'B' AS p2
/*UNION ALL
SELECT   0 AS id ,
'A' AS p1 ,
'B' AS p2*/
UNION ALL
SELECT   2 AS id ,
'C' AS p1 ,
'D' AS p2
UNION ALL
SELECT   3 AS id ,
'E' AS p1 ,
'F' AS p2
UNION ALL
SELECT   4 AS id ,
'D' AS p1 ,
'C' AS p2
UNION ALL
SELECT   5 AS id ,
'B' AS p1 ,
'A' AS p2
UNION ALL
SELECT   6 AS id ,
'H' AS p1 ,
'J' AS p2
UNION ALL
SELECT   7 AS id ,
'T' AS p1 ,
'U' AS p2
UNION ALL
SELECT   8 AS id ,
'J' AS p1 ,
'H' AS p2
/*UNION ALL
SELECT   9 AS id ,
'I' AS p1 ,
'L' AS p2
UNION ALL
SELECT   10 AS id ,
'J' AS p1 ,
'K' AS p2*/
),
c2
AS ( SELECT   MIN(id) AS min_id
FROM     c1
GROUP BY ASCII(p1) + ASCII(p2)
)
SELECT  c1.*
FROM    c1
JOIN c2 ON id = min_id

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咋一看，似乎也可以实现同样的需求。实际上，这种写法存在2个问题：

　　1.如果p1,p2是多个字符，ASCII的方式只会取第一个字符的ASCII

　　2.ASCII('A')+ASCII('D')=ASCII('B')+ASCII('C'),对于这样的数据，用ASCII的方式无法区分

(本文完)