Question

我有两张桌子。其中一个条目如下：

User_ID     Cat_ID

1           [1,2]
2           [1]
3           [3]

另一方面，我有与类别ID相关联的字符串：

Cat_ID      Cat_Name
1           Category1
2           Category2
3           Category3

我希望能够在CatID上执行连接，所以我得到了类似的内容：

User_ID    Category_ID
1          ['Category1', 'Category2']   
2          ['Category1']
3          ['Category3']

我理解列上的连接，如果该列只有单个条目以允许一对一映射，但是如何为同一列执行多对一映射？

Answer 1

为了将值拆分为列，我们需要创建函数

create function [dbo].[udf_splitstring] (@tokens    varchar(max),
                                             @delimiter varchar(5))
    returns @split table (
      token varchar(200) not null )
    as
      begin
          declare @list xml

          select @list = cast('<a>'
                              + replace(@tokens, @delimiter, '</a><a>')
                              + '</a>' as xml)

          insert into @split
                      (token)
          select ltrim(t.value('.', 'varchar(200)')) as data
          from   @list.nodes('/a') as x(t)

          return
      end


    create table #a
    (
        User_ID int,     Cat_ID varchar(10)
    )
    insert into #a values
    (1,'1,2'),
    (2,'1'),
    (3,'3')


    create table #b
    (
        Cat_ID int,      Cat_Name varchar(50)
    )
    insert into #b values

    (1,'Category1'),
    (2,'Category2'),
    (3,'Category3')



    ;WITH CTE AS
    (
    SELECT USER_ID,B.CAT_NAME FROM (SELECT T.USER_ID,CAST(X.TOKEN AS INT) AS CAT_ID 
        FROM #A T
        CROSS APPLY (SELECT TOKEN FROM [UDF_SPLITSTRING](T.CAT_ID,',') ) X)C
        JOIN (SELECT * FROM #B) B ON B.CAT_ID=C.CAT_ID
        )

        SELECT  USER_ID
           ,STUFF((SELECT ', ' + CAST(CAT_NAME AS VARCHAR(10)) [text()]
             FROM cte 
             WHERE USER_ID = t.USER_ID
             FOR XML PATH(''), TYPE)
            .value('.','NVARCHAR(MAX)'),1,2,' ') Category_ID
    FROM cte t
    GROUP BY USER_ID

USER_ID  Category_ID
1        Category1, Category2
2        Category1
3        Category3

加入可以有多个条目SQL的列

1 个答案: