行列互转，是一个经常遇到的需求。实现的方法，有case when方式和2005之后的内置pivot和unpivot方法来实现。
在读了技术内幕那一节后，虽说这些解决方案早就用过了，却没有系统性的认识和总结过。为了加深认识，再总结一次。
行列互转，可以分为静态互转，即事先就知道要处理多少行（列）;动态互转,事先不知道处理多少行(列)。

--创建测试环境USE tempdb;GOIF OBJECT_ID('dbo.Orders') IS NOT NULL DROP TABLE dbo.Orders;GOCREATE TABLE dbo.Orders( orderid int NOT NULL PRIMARY KEY NONCLUSTERED, orderdate datetime NOT NULL, empid int NOT NULL, custid varchar(5) NOT NULL, qty int NOT NULL);CREATE UNIQUE CLUSTERED INDEX idx_orderdate_orderid ON dbo.Orders(orderdate, orderid);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(30001, '20020802', 3, 'A', 10);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(10001, '20021224', 1, 'A', 12);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(10005, '20021224', 1, 'B', 20);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(40001, '20030109', 4, 'A', 40);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(10006, '20030118', 1, 'C', 14);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(20001, '20030212', 2, 'B', 12);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(40005, '20040212', 4, 'A', 10);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(20002, '20040216', 2, 'C', 20);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(30003, '20040418', 3, 'B', 15);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(30004, '20020418', 3, 'C', 22);INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty) VALUES(30007, '20020907', 3, 'D', 30);GO

行转列-静态方案：

--行转列的静态方案一：CASE WHEN,兼容sql2000select custid,sum(case when YEAR(orderdate)=2002 then qty end) as [2002],sum(case when YEAR(orderdate)=2003 then qty end) as [2003],sum(case when YEAR(orderdate)=2004 then qty end) as [2004]from ordersgroup by custid;GO--行转列的静态方案二：PIVOT,sql2005及以后版本select *from (select custid,YEAR(orderdate) as years,qty from orders) as ordpivot(sum(qty) for years in([2002],[2003],[2004]))as pGO

行转列-动态方案：加入了xml处理和SQL注入预防判断

--既然是用到了动态SQL,就有一个老话题:SQL注入。建一个注入性字符的判断函数。CREATE FUNCTION [dbo].[fn_CheckSQLInjection]( @Col nvarchar(4000))RETURNS BIT --如果存在可能的注入字符返回true,反之返回falseASBEGINDECLARE @result bit; IF UPPER(@Col) LIKE UPPER(N'%0x%') OR UPPER(@Col) LIKE UPPER(N'%;%') OR UPPER(@Col) LIKE UPPER(N'%''%') OR UPPER(@Col) LIKE UPPER(N'%--%') OR UPPER(@Col) LIKE UPPER(N'%%') OR UPPER(@Col) LIKE UPPER(N'%EXEC%') OR UPPER(@Col) LIKE UPPER(N'%xp_%') OR UPPER(@Col) LIKE UPPER(N'%sp_%') OR UPPER(@Col) LIKE UPPER(N'%SELECT%') OR UPPER(@Col) LIKE UPPER(N'%INSERT%') OR UPPER(@Col) LIKE UPPER(N'%UPDATE%') OR UPPER(@Col) LIKE UPPER(N'%DELETE%') OR UPPER(@Col) LIKE UPPER(N'%TRUNCATE%') OR UPPER(@Col) LIKE UPPER(N'%CREATE%') OR UPPER(@Col) LIKE UPPER(N'%ALTER%') OR UPPER(@Col) LIKE UPPER(N'%DROP%') SET @result=1 ELSE SET @result=0 return @resultENDGO--行转列的动态方案一：CASE WHEN,兼容sql2000DECLARE @T TABLE (years INT NOT NULL PRIMARY KEY);INSERT INTO @T SELECT DISTINCT YEAR(orderdate) from orders;DECLARE @Y INT;SET @Y=(SELECT MIN(years) from @T);DECLARE @SQL NVARCHAR(4000)=N'';WHILE @Y IS NOT NULLBEGIN SET @SQL=@SQL+N',sum(case when YEAR(orderdate)='+CAST(@Y AS NVARCHAR(4)) +N' then qty end) as '+QUOTENAME(@Y); SET @Y=(SELECT MIN(years) from @T where years>@Y);ENDIF dbo.fn_CheckSQLInjection(@SQL)=0SET @SQL=N'SELECT custid'+@SQL+N' FROM orders group by custid'PRINT @SQLEXEC sp_executesql @SQLGO--行转列的动态方案二：PIVOT,sql2005及以后版本DECLARE @T TABLE (years INT NOT NULL PRIMARY KEY);INSERT INTO @T SELECT DISTINCT YEAR(orderdate) from orders;DECLARE @Y INT;SET @Y=(SELECT MIN(years) from @T);DECLARE @SQL NVARCHAR(4000)=N''; --这里使用了xml处理来处理类组字符串SET @SQL=STUFF((SELECT N','+QUOTENAME(years) FROM @T FOR XML PATH('')),1,1,N'');IF dbo.fn_CheckSQLInjection(@SQL)=0SET @SQL=N'select * from (select DISTINCT custid,YEAR(orderdate) as years,qty from orders) as ordpivot(sum(qty) for years in('+@SQL+N'))as p';PRINT @SQL;EXEC SP_EXECUTESQL @SQL;GO

列转行：

--列转行的静态方案：UNPIVOT,sql2005及以后版本SELECT * FROM dbo.pvtCustOrdersSELECT custid,years,qtyfrom dbo.pvtCustOrdersunpivot(qty for years in([2002],[2003],[2004]))as upGO--列转行的动态方案：UNPIVOT,sql2005及以后版本--因为行是动态所以这里就从INFORMATION_SCHEMA.COLUMNS视图中获取列来构造行，同样也使用了XML处理。DECLARE @SQL NVARCHAR(4000)=N'';SET @SQL=STUFF((SELECT N','+QUOTENAME(COLUMN_NAME ) FROM INFORMATION_SCHEMA.COLUMNSWHERE ORDINAL_POSITION>1 AND TABLE_NAME='PvtCustOrders'FOR XML PATH('')),1,1,N'')SET @SQL=N'SELECT custid,years,qty from dbo.pvtCustOrders unpivot(qty for years in('+@SQL+'))as up';PRINT @SQL;EXEC SP_EXECUTESQL @SQL;

总结

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