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