讲解数据库中行级转换成列级的实际应用

create table score
(
   Name    varchar(10),
   Subject varchar(10),
   Result int
)
go
 
-- Insert some data to score table
insert into score(Name , Subject , Result) values('Jason' , 'Chinese' , 74)
insert into score(Name , Subject , Result) values('Jason' , 'Math' , 83)
insert into score(Name , Subject , Result) values('Jason' , 'Physic' , 93)
insert into score(Name , Subject , Result) values('Bosco' , 'Chinese' , 74)
insert into score(Name , Subject , Result) values('Bosco' , 'Math' , 84)
insert into score(Name , Subject , Result) values('Bosco' , 'Physic' , 94)
go
 
-- useing PIVOT operator
SELECT * FROM
(    
    select Name,Subject,Result from score
) as X
PIVOT
(    
   Sum(Result) FOR Subject IN ([Chinese],[Math],[Physic])
) AS PVT
 
-- useing static SQL. There only are [Chinese],
[Math],[Physic] values in subject field
select Name,
 sum(case Subject when 'Chinese' then Result else 0 end) as [Chinese],
 sum(case Subject when 'Math' then Result else 0 end) as [Math],
 sum(case Subject when 'Physic' then Result else 0 end) as [Physic]
from score
group by Name
 
-- useing dynamic SQL. There may be some other 
values in subject field,don't limited to [Chinese],[Math],[Physic]
declare @sql varchar(2000)
set @sql = 'select Name'
select @sql = @sql + ', sum(case Subject when 
''' + Subject + ''' then Result else 0 end) [' + Subject + ']'
from (select distinct Subject from score) as X
set @sql = @sql + ' from score group by Name'
exec(@sql)