【SQLServer系列教程】——邏輯控制語句

1.邏輯控制語句類型

2.IF-ELSE語句

3.WHILE語句

4.CASE-END語句

5.案例代碼：

示例1：IF-ELSE語句示例

use StudentManageDB
go
--查詢成績
declare @cAvg int
select @cAvg=avg(CSharp) from ScoreList 
inner join Students on ScoreList.StudentId=Students.StudentId where ClassId=1
print 'C#平均成績：'+convert(varchar(20),@cAvg)
--判斷成績
if(@cAvg>=80)  
	print '軟件一班成績優秀！'  
else
	print '軟件一班成績一般！'

示例2：WHILE語句示例

use StudentManageDB
go
print '加分之前的C#成績：'
select StudentId,CSharp from ScoreList 
declare @CSharp int,@StuId int
while(1=1)
	begin
		select top 1 @CSharp=CSharp,@StuId=StudentId 
                 from ScoreList where CSharp<60
       if (@CSharp<60) 
          update ScoreList set CSharp=CSharp+1 
                where StudentId=@StuId
       if((select count(*) from ScoreList where CSharp<60)=0)
         break
   end
print '加分之後的C#成績：'
select StudentId,CSharp from ScoreList 

示例3：CASE-END語句示例

use StudentManageDB
go
select 學號=StudentId,
總評=CASE
				when (CSharp+SQLServerDB)/2>=90 then  'A'  
				when (CSharp+SQLServerDB)/2 between 80 and 89 then  'B'  
				when (CSharp+SQLServerDB)/2 between 70 and 79 then  'C'  
				when (CSharp+SQLServerDB)/2 between 60 and 69 then  'D' 
				else '不及格' 
          end
from ScoreList