引:
???????? 为了举例说明,这里创建了一张成绩表,如下图所示:
???????? 
比较:
???????? 1、sql中,这两个函数我们仅能使用case,代码及结果如下:
?? select name,
?????? case Subject
????????? when '语文' then 1
????????? when '数学' then 2
????????? when '英语' then 3?? --else 3
?????? end? as '科目代码'
?? from Results
?? 
?? 同样的,我们可以用case实现行转列,代码及结果如下:
?? select Name,
??????????? sum(case when Subject='语文' then Result end) '语文',
??????????? sum(case when Subject='数学' then Result end) '数学',
??????????? sum(case when Subject='英语' then Result end) '英语'
?? from Results
?? group by Name
?? 
??
???????? 2、但是,在oracle中,这两个函数我们都可以使用,代码及结果如下:
???????????? decode用法：select Name,decode(Subject,'语文',1,'数学',2,'英语',3) 科目代码 from results;
???????????????????????????????select Name,decode(Subject,'语文',1,'数学',2,3) 科目代码?from Results;
???????????????? case用法：
? select name,
?????? case
????????? when Subject='语文' then 1
????????? when Subject='数学' then 2
????????? when Subject='英语' then 3? --else 3
?????? end? as 科目代码
? from Results;
? 这两种方法均能达到同样的结果:
? 
? 同样的,我们可以使用这两个函数实现行转列,代码及结果如下:
? decode:
select
?? Name,
?? sum(decode(Subject,'语文',Result,0)) 语文,
?? sum(decode(Subject,'数学',Result,0)) 数学,
?? sum(decode(Subject,'英语',Result,0)) 英语
from Results
group by Name;
?????case:
select
?? Name,
?? sum((case when Subject='语文' then Result else 0 end)) 语文,
?? sum((case when Subject='数学' then Result else 0 end)) 数学,
?? sum((case when Subject='英语' then Result else 0 end)) 英语
from Results
group by Name;
?
数据库表与行转列的中间结果(想想还是也附上)
oracle中:
select
?? Name,
?? decode(Subject,'语文',Result,0) 语文,
?? decode(Subject,'数学',Result,0) 数学,
?? decode(Subject,'英语',Result,0) 英语
from Results;
或
select
?? Name,
?? (case when Subject='语文' then Result else 0 end) 语文,
?? (case when Subject='数学' then Result else 0 end) 数学,
?? (case when Subject='英语' then Result else 0 end) 英语
from Results;?
结果如下:
以上内容,不对的地方请指正。此文仅想抛砖引玉...
(续)
SQL2000中动态SQL
declare @sql varchar(8000)
set @sql = 'select name '
select @sql = @sql + ' , sum(case Subject when '+ char(39) + Subject + char(39) +' then Result else 0 end) [' + Subject + ']'
from (select distinct Subject from results) as a
set @sql = @sql + ' from results group by name'
exec(@sql)
?
SQL2005中动态SQL
declare @sql varchar(8000)
select @sql = isnull(@sql + '],[' , '') + Subject from Results group by Subject
set @sql = '[' + @sql + ']'
exec ('select * from? Results pivot (max(result) for subject in (' + @sql + ')) b')
?
注：引用自? http://www.cnblogs.com/NothingIsImpossible/archive/2010/10/13/1850250.html