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03. 行列转换写法小结

2024-07-09 05:34:17   218人阅读

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 RowToColcreate table RowToCol(ID int,Code varchar(10),Value int)Goinsert RowToCol select 1,‘Item1‘,1000 union allselect 1,‘Item2‘,1000 union allselect 1,‘Item3‘,500 union allselect 2,‘Item1‘,2000 union allselect 2,‘Item2‘,0 union allselect 3,‘Item1‘,1000 union allselect 3,‘Item3‘,500 GOselect * from RowToCol

 要得到这样的结果：

IDItem1Item2Item3
110001000500
2200000
310000500


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 Item3from 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 Item3from 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 aset @sql = @sql + ‘ from RowToCol group by ID‘--print @sqlexec(@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 Codeset @sql = ‘[‘ + @sql + ‘]‘--print @sqlexec (‘select * from (select * from RowToCol) a pivot (max(value) for Code in (‘ + @sql + ‘)) b‘)

 

二. 列转行

--drop table ColToRowcreate table ColToRow(ID int,Item1 int,Item2 int,Item3 int)GOinsert into ColToRowselect ‘1‘,1000,1000,500 union allselect ‘2‘,2000,0,0 union allselect ‘3‘,1000,0,500 GOselect * from ColToRow

 要得到这样的结果：

IDCodeValue
1Item11000
1Item21000
1Item3500
2Item12000
2Item20
2Item30
3Item11000
3Item20
3Item3500

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 ColToRowunion allselect ID,Code=‘Item2‘,Value=Item2 from ColToRowunion allselect ID,Code=‘Item3‘,Value=Item3 from ColToRoworder 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 @sqlexec(@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 @sqlexec(‘select ID , Code , Value from ColToRow unpivot (Value for Code in(‘ + @sql + ‘)) t‘)

 

 


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