T-SQL 逻辑控制语句 ifelse while casewhen

ifelse,如果逻辑语句有多行,用begin end 包裹

 use StudentManageDB
 go
 --查询成绩
 declare @cAvg int
 select @cAvg=avg(CSharp) from ScoreList
 inner join Students on ScoreList.StudentId=Students.StudentId where ClassId=1
 print 'C#平均成绩：'+convert(varchar(20),@cAvg)
 --判断成绩
 if(@cAvg>=80)
     print '软件一班成绩优秀！'
 else
     print '软件一班成绩一般！'

while,如果逻辑语句有多行,用begin end 包裹

 use StudentManageDB
 go
 print '加分之前的C#成绩：'
 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 '加分之后的C#成绩：'
 select StudentId,CSharp from ScoreList 

case when

 use StudentManageDB
 go
 select 学号=StudentId,
 总评=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