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)。
1 --创建测试环境
2 USE tempdb;
3 GO
4
5 IF OBJECT_ID('dbo.Orders') IS NOT NULL
6 DROP TABLE dbo.Orders;
7 GO
8
9 CREATE TABLE dbo.Orders
10 (
11 orderid int NOT NULL PRIMARY KEY NONCLUSTERED,
12 orderdate datetime NOT NULL,
13 empid int NOT NULL,
14 custid varchar(5) NOT NULL,
15 qty int NOT NULL
16 );
17
18 CREATE UNIQUE CLUSTERED INDEX idx_orderdate_orderid
19 ON dbo.Orders(orderdate, orderid);
20
21 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
22 VALUES(30001, '20020802', 3, 'A', 10);
23 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
24 VALUES(10001, '20021224', 1, 'A', 12);
25 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
26 VALUES(10005, '20021224', 1, 'B', 20);
27 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
28 VALUES(40001, '20030109', 4, 'A', 40);
29 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
30 VALUES(10006, '20030118', 1, 'C', 14);
31 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
32 VALUES(20001, '20030212', 2, 'B', 12);
33 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
34 VALUES(40005, '20040212', 4, 'A', 10);
35 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
36 VALUES(20002, '20040216', 2, 'C', 20);
37 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
38 VALUES(30003, '20040418', 3, 'B', 15);
39 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
40 VALUES(30004, '20020418', 3, 'C', 22);
41 INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
42 VALUES(30007, '20020907', 3, 'D', 30);
43 GO
行转列-静态方案：
1 --行转列的静态方案一：CASE WHEN,兼容sql2000
2 select custid,
3 sum(case when YEAR(orderdate)=2002 then qty end) as [2002],
4 sum(case when YEAR(orderdate)=2003 then qty end) as [2003],
5 sum(case when YEAR(orderdate)=2004 then qty end) as [2004]
6 from orders
7 group by custid;
8 GO
9 --行转列的静态方案二：PIVOT,sql2005及以后版本
10 select *
11 from (select custid,YEAR(orderdate) as years,qty from orders) as ord
12 pivot(sum(qty) for years in([2002],[2003],[2004]))as p
13 GO
行转列-动态方案：加入了xml处理和SQL注入预防判断
1 --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。
2 CREATE FUNCTION [dbo].[fn_CheckSQLInjection]
3 (
4 @Col nvarchar(4000)
5 )
6 RETURNS BIT --如果存在可能的注入字符返回true,反之返回false
7 AS
8 BEGIN
9 DECLARE @result bit;
10 IF
11 UPPER(@Col) LIKE UPPER(N'%0x%')
12 OR UPPER(@Col) LIKE UPPER(N'%;%')
13 OR UPPER(@Col) LIKE UPPER(N'%''%')
14 OR UPPER(@Col) LIKE UPPER(N'%--%')
15 OR UPPER(@Col) LIKE UPPER(N'%/*%*/%')
16 OR UPPER(@Col) LIKE UPPER(N'%EXEC%')
17 OR UPPER(@Col) LIKE UPPER(N'%xp_%')
18 OR UPPER(@Col) LIKE UPPER(N'%sp_%')
19 OR UPPER(@Col) LIKE UPPER(N'%SELECT%')
20 OR UPPER(@Col) LIKE UPPER(N'%INSERT%')
21 OR UPPER(@Col) LIKE UPPER(N'%UPDATE%')
22 OR UPPER(@Col) LIKE UPPER(N'%DELETE%')
23 OR UPPER(@Col) LIKE UPPER(N'%TRUNCATE%')
24 OR UPPER(@Col) LIKE UPPER(N'%CREATE%')
25 OR UPPER(@Col) LIKE UPPER(N'%ALTER%')
26 OR UPPER(@Col) LIKE UPPER(N'%DROP%')
27 SET @result=1
28 ELSE
29 SET @result=0
30 return @result
31 END
32 GO
33
34 --行转列的动态方案一：CASE WHEN,兼容sql2000
35 DECLARE @T TABLE (years INT NOT NULL PRIMARY KEY);
36 INSERT INTO @T
37 SELECT DISTINCT YEAR(orderdate) from orders;
38 DECLARE @Y INT;
39 SET @Y=(SELECT MIN(years) from @T);
40 DECLARE @SQL NVARCHAR(4000)=N'';
41 WHILE @Y IS NOT NULL
42 BEGIN
43 SET @SQL=@SQL+N',sum(case when YEAR(orderdate)='+CAST(@Y AS NVARCHAR(4)) +N' then qty end) as '+QUOTENAME(@Y);
44 SET @Y=(SELECT MIN(years) from @T where years>@Y);
45 END
46 IF dbo.fn_CheckSQLInjection(@SQL)=0
47 SET @SQL=N'SELECT custid'+@SQL+N' FROM orders group by custid'
48 PRINT @SQL
49 EXEC sp_executesql @SQL
50 GO
51
52 --行转列的动态方案二：PIVOT,sql2005及以后版本
53 DECLARE @T TABLE (years INT NOT NULL PRIMARY KEY);
54 INSERT INTO @T
55 SELECT DISTINCT YEAR(orderdate) from orders;
56 DECLARE @Y INT;
57 SET @Y=(SELECT MIN(years) from @T);
58 DECLARE @SQL NVARCHAR(4000)=N'';
59
60 --这里使用了xml处理来处理类组字符串
61 SET @SQL=STUFF((SELECT N','+QUOTENAME(years) FROM @T
62 FOR XML PATH('')),1,1,N'');
63 IF dbo.fn_CheckSQLInjection(@SQL)=0
64 SET @SQL=N'select * from (select DISTINCT custid,YEAR(orderdate) as years,qty from orders) as ord
65 pivot(sum(qty) for years in('+@SQL+N'))as p';
66 PRINT @SQL;
67 EXEC SP_EXECUTESQL @SQL;
68 GO
列转行：
1 --列转行的静态方案：UNPIVOT,sql2005及以后版本
2 SELECT * FROM dbo.pvtCustOrders
3 SELECT custid,years,qty
4 from dbo.pvtCustOrders
5 unpivot(qty for years in([2002],[2003],[2004]))as up
6 GO
7 --列转行的动态方案：UNPIVOT,sql2005及以后版本
8 --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。
9 DECLARE @SQL NVARCHAR(4000)=N'';
10 SET @SQL=STUFF((SELECT N','+QUOTENAME(COLUMN_NAME ) FROM INFORMATION_SCHEMA.COLUMNS
11 WHERE ORDINAL_POSITION>1 AND TABLE_NAME='PvtCustOrders'
12 FOR XML PATH('')),1,1,N'')
13 SET @SQL=N'SELECT custid,years,qty
14 from dbo.pvtCustOrders
15 unpivot(qty for years in('+@SQL+'))as up';
16 PRINT @SQL;
17 EXEC SP_EXECUTESQL @SQL;