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)。
sql;">
--创建测试环境
USE tempdb;
GO
IF OBJECT_ID('dbo.Orders') IS NOT NULL
DROP TABLE dbo.Orders;
GO
CREATE 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,qty)
VALUES(10001,'20021224',1,12);
INSERT INTO dbo.Orders(orderid,qty)
VALUES(10005,'B',20);
INSERT INTO dbo.Orders(orderid,qty)
VALUES(40001,'20030109',4,40);
INSERT INTO dbo.Orders(orderid,qty)
VALUES(10006,'20030118','C',14);
INSERT INTO dbo.Orders(orderid,qty)
VALUES(20001,'20030212',2,qty)
VALUES(40005,'20040212',qty)
VALUES(20002,'20040216',qty)
VALUES(30003,'20040418',15);
INSERT INTO dbo.Orders(orderid,qty)
VALUES(30004,'20020418',22);
INSERT INTO dbo.Orders(orderid,qty)
VALUES(30007,'20020907','D',30);
GO
行转列-静态方案：
sql;">
--行转列的静态方案一：CASE WHEN,兼容sql2000
select 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 orders
group 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 ord
pivot(sum(qty) for years in([2002],[2003],[2004]))as p
GO
行转列-动态方案：加入了xml处理和sql注入预防判断
@Y);
END
IF dbo.fn_ChecksqlInjection(@sql)=0
SET @sql=N'SELECT custid'+@sql+N' FROM orders group by custid'
PRINT @sql
EXEC sp_executesql @sql
GO
--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('')),N'');
IF dbo.fn_ChecksqlInjection(@sql)=0
SET @sql=N'select * from (select DISTINCT custid,qty from orders) as ord
pivot(sum(qty) for years in('+@sql+N'))as p';
PRINT @sql;
EXEC SP_EXECUTEsql @sql;
GO
列转行：
1 AND TABLE_NAME='PvtCustOrders'
FOR XML PATH('')),N'')
SET @sql=N'SELECT custid,qty
from dbo.pvtCustOrders
unpivot(qty for years in('+@sql+'))as up';
PRINT @sql;
EXEC SP_EXECUTEsql @sql;
总结
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