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  • 将字符串中的重复字符剔除

    数据库环境:SQL SERVER2008R2

    在网上看到一网友提的需求,要求把字符串列中的重复字符剔除,只保留一个。我简单的把需求描述下,

    比如,有一个t表,A1列存字符串,存储的内容如下:

    A1

    A,B,B,C

    C,C,D

    F,S,S

    剔除重复字符后的结果如下:

    A1

    A,B,C

    C,D

    F,S

    思路:每一行记录生成一个行号,把字符串中的字符全部存到一列,根据行号和字符去重,然后再用FOR XML PATH合并到一行

    /*数据准备*/
    WITH    x0
              AS ( SELECT   1 AS id ,
                            'A,B,B,C' AS A1
                   UNION ALL
                   SELECT   2 AS id ,
                            'C,C,D' AS A1
                   UNION ALL
                   SELECT   3 AS id ,
                            'F,S,S' AS A1
                 ),/*将所有字符转存一列,去重*/
            x2
              AS ( SELECT  DISTINCT
                            a.id ,
                            SUBSTRING(a.A1, b.number,
                                      CHARINDEX(',', a.A1 + ',', b.number)
                                      - b.number) AS A1
                   FROM     x0 a ,
                            master..spt_values b
                   WHERE    b.number >= 1
                            AND b.number <= LEN(a.A1)
                            AND b.type = 'P'
                            AND SUBSTRING(',' + a.A1, b.number, 1) = ','
                 )
         /*根据原先的行号,把行号相同的转回到一行上*/
        SELECT  LEFT(A1, LEN(A1) - 1) AS A1
        FROM    ( SELECT    id ,
                            ( SELECT    a.A1 + ','
                              FROM      x2 a
                              WHERE     a.id = b.id
                            FOR
                              XML PATH('')
                            ) AS A1
                  FROM      x2 b
                  GROUP BY  id
                ) t

    SQL比较好理解,并加了一些注释,这里不再重复。

    (全文完)

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  • 原文地址:https://www.cnblogs.com/boss-he/p/4553855.html
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