SQL行转列和列转行代码详解
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;
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, 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
--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false
AS
BEGIN
DECLARE @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 @result
END
GO
--行转列的动态方案一：CASE WHEN,兼容sql2000
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'';
WHILE @Y IS NOT NULL
BEGIN
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);
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('')),1,1,N'');
IF dbo.fn_CheckSQLInjection(@SQL)=0
SET @SQL=N'select * from (select DISTINCT custid,YEAR(orderdate) as years,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：
--列转行的静态方案：UNPIVOT,sql2005及以后版本
SELECT * FROM dbo.pvtCustOrders
SELECT custid,years,qty
from dbo.pvtCustOrders
unpivot(qty for years in([2002],[2003],[2004]))as up
GO
--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.COLUMNS
WHERE 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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