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原文:03. 行列转换写法小结行列转换，通常有2种方法，一是CASE WHEN/UNION；一是PIVOT/UNPIVOT。对于行值或列数不固定的情况，需要用动态SQL。
一. 行转列
--drop table RowToCol create table RowToCol ( ID int, Code varchar(10), Value int ) Go insert RowToCol select 1,‘Item1‘,1000 union all select 1,‘Item2‘,1000 union all select 1,‘Item3‘,500 union all select 2,‘Item1‘,2000 union all select 2,‘Item2‘,0 union all select 3,‘Item1‘,1000 union all select 3,‘Item3‘,500 GO select * from RowToCol
要得到这样的结果：
| ID | Item1 | Item2 | Item3 |
| 1 | 1000 | 1000 | 500 |
| 2 | 2000 | 0 | 0 |
| 3 | 1000 | 0 | 500 |
1. CASE WHEN
在SQL Server 2000时，常用的写法，沿用至今。
(1) 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
(2) 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. PIVOT
PIVOT是SQL Server 2005的新语法，Oracle在11g中也推出了这个语法。
(1) 静态
select * from (select * from RowToCol) a pivot (max(value) for Code in ([Item1],[Item2],[Item3])) b
(2) 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‘)
二. 列转行
--drop table ColToRow create table ColToRow ( ID int, Item1 int, Item2 int, Item3 int ) GO insert into ColToRow select ‘1‘,1000,1000,500 union all select ‘2‘,2000,0,0 union all select ‘3‘,1000,0,500 GO select * from ColToRow
要得到这样的结果：
| ID | Code | Value |
| 1 | Item1 | 1000 |
| 1 | Item2 | 1000 |
| 1 | Item3 | 500 |
| 2 | Item1 | 2000 |
| 2 | Item2 | 0 |
| 2 | Item3 | 0 |
| 3 | Item1 | 1000 |
| 3 | Item2 | 0 |
| 3 | Item3 | 500 |
1. UNION
在SQL Server 2000时，常用的写法，沿用至今。
(1) 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。
(2) 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. UNPIVOT
UNPIVOT是SQL Server 2005的新语法，Oracle在11g中也推出了这个语法。
(1) 静态
select ID , Code , Value from ColToRow unpivot (Value for Code in([Item1] , [Item2] , [Item3])) t
(2) 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‘)
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原文地址：http://www.cnblogs.com/lonelyxmas/p/3959241.html
