行列转换小结 Pivot ，Unpivot （转，改）

行专列 Pivot

1）SQL 2000版本

静态

SELECT  ID ,
        SUM(CASE Code
              WHEN 'Item1' THEN Value
              ELSE 0
            END) AS Item1 ,
        SUM(CASE Code
              WHEN 'Item2' THEN Value
              ELSE 0
            END) AS Item2 ,
        SUM(CASE Code
              WHEN 'Item3' THEN Value
              ELSE 0
            END) AS Item3
FROM    RowToCol
GROUP BY ID
--或者用max也行
SELECT  ID ,
        MAX(CASE Code
              WHEN 'Item1' THEN Value
              ELSE 0
            END) AS Item1 ,
        MAX(CASE Code
              WHEN 'Item2' THEN Value
              ELSE 0
            END) AS Item2 ,
        MAX(CASE Code
              WHEN 'Item3' THEN Value
              ELSE 0
            END) AS Item3
FROM    RowToCol
GROUP BY ID

动态

在不确定有多少行需要转为列时，先distinct出待转列的值，再拼出包含若干个CASE的SQL语句，然后运行。

DECLARE @sql VARCHAR(8000)
SET @sql = 'select ID '
SELECT  @sql = @sql + ' , max(case Code when ''' + Code
        + ''' then Value else 0 end) [' + Code + ']'
FROM    ( SELECT DISTINCT
                    Code
          FROM      RowToCol
        ) AS a
SET @sql = @sql + ' from RowToCol group by ID'
--print @sql
EXEC(@sql)

2） SQL 2005以后版本

PIVOT是SQL Server 2005的新语法，Oracle在11g中也推出了这个语法。

静态

SELECT  custid ,
        [] ,
        [] ,
        []
FROM    Sales.Orders PIVOT( SUM(freight) FOR shipperid IN ( [], [], [] ) ) AS P;

分解

结果

动态

用PIVOT拼写动态SQL时就简单了，只要把后面的列清单整理出来就可以了。

DECLARE @sql VARCHAR(8000)
SELECT  @sql = ISNULL(@sql + '],[', '') + Code
FROM    RowToCol
GROUP BY Code
SET @sql = '[' + @sql + ']'
--print @sql
EXEC ('select * from (select * from RowToCol) a pivot (max(value) for Code in (' + @sql + ')) b')

列转行 UNPIVOT

1）SQL Server 2000版

静态

SELECT  ID ,
        Code = 'Item1' ,
        Value = Item1
FROM    ColToRow
UNION ALL
SELECT  ID ,
        Code = 'Item2' ,
        Value = Item2
FROM    ColToRow
UNION ALL
SELECT  ID ,
        Code = 'Item3' ,
        Value = Item3
FROM    ColToRow
ORDER BY ID

SQL Server对于多个UNION的排序，只要在最后加ORDER BY就可以了。

动态

在不确定有多少列需要转为行时，先借助系统表syscolumns找出待转行的列，再拼出包含若干个UNION语句，然后运行。

DECLARE @sql VARCHAR(8000)
SELECT  @sql = ISNULL(@sql + ' union all ', '') + ' select ID , [Code] = '
        + QUOTENAME(name, '''') + ' , [Value] = ' + QUOTENAME(name)
        + ' from ColToRow'
FROM    syscolumns
WHERE   name <> N'ID'
        AND id = OBJECT_ID('ColToRow')
ORDER BY colid ASC
--print @sql
EXEC(@sql + ' order by ID ')

2） SQL 2005以后版本

静态

创建样本

-- sample data for UNPIVOT example
USE TSQL2012;
IF OBJECT_ID(N'Sales.FreightTotals', N'U') IS NOT NULL DROP TABLE Sales.FreightTotals;
GO

WITH PivotData AS
(
  SELECT
    custid   , -- grouping column
    shipperid, -- spreading column
    freight    -- aggregation column
  FROM Sales.Orders
)
SELECT *
INTO Sales.FreightTotals
FROM PivotData
  PIVOT( SUM(freight) FOR shipperid IN ([],[],[]) ) AS P;

UNPIVOT

SELECT  *
FROM    Sales.FreightTotals;
-- unpivot data
SELECT  custid ,
        shipperid ,
        freight
FROM    Sales.FreightTotals UNPIVOT( freight FOR shipperid IN ( [], [], [] ) ) AS U;

动态

DECLARE @sql VARCHAR(8000)
SELECT  @sql = ISNULL(@sql + '],[', '') + name
FROM    syscolumns
WHERE   name <> N'ID'
        AND id = OBJECT_ID('ColToRow')
SET @sql = '[' + @sql + ']'
--print @sql
EXEC('select ID , Code , Value from ColToRow unpivot (Value for Code in(' + @sql + ')) t')

参考文档

03. 行列转换写法小结