如何在SQL Server中使用CTE连接字符串？

Question

使用CTE或公用表表达式，如何跨多行连接字符串。

Answer 1

1. 按州分列县（NumberedCounties）
2. 选择每个州的第一个县（JoinedCounties，RowNumber = 1）
3. 选择每个州的第二个县（JoinedCounties，RowNumber = RowNumber + 1）
4. 获取最大行号（WithMax）
5. 按最大行数过滤
6. 确保不超过递归限制。

   WITH    NumberedCounties(RowNumber, County, State)
              AS (SELECT    ROW_NUMBER() OVER (PARTITION BY C.State ORDER BY c.County),
                            c.County,
                            c.State
                  FROM      Static.County C
                 ),
            JoinedCounties(RowNumber, Counties, State)
              AS (SELECT    RowNumber,
                            CONVERT(VARCHAR(4000), County),
                            State
                  FROM      NumberedCounties
                  WHERE     RowNumber = 1
                  UNION ALL
                  SELECT    C.RowNumber,
                            CONVERT(VARCHAR(4000), R.Counties + ', '
                            + C.County),
                            C.State
                  FROM      JoinedCounties R
                            INNER JOIN NumberedCounties C ON R.State = C.State
                                                             AND C.RowNumber = (R.RowNumber
                                                                  + 1)
                 ),
            WithMax(Counties, State, RowNumber, MaxRowNumber)
              AS (SELECT    Counties,
                            State,
                            RowNumber,
                            MAX(RowNumber) OVER (PARTITION BY State) AS MaxRowNumber
                  FROM      JoinedCounties
                 )
        SELECT  Counties,
                State
        FROM    WithMax
        WHERE   RowNumber = MaxRowNumber
    OPTION  (MAXRECURSION 500);

注意：如果你有一些非常重要的记录，那么与在应用程序中连接记录相比，这将会非常慢。