sqlserver in 和 exist 子查询

1 in 子查询

use StudentManageDB
go
--select StudentName from Students 
--where StudentId=(select StudentId from ScoreList where SQLServerDB>80)
select StudentName from Students 
where StudentId in (select StudentId from ScoreList where SQLServerDB>80)

use StudentManageDB
go
select StudentId,StudentName from Students
where StudentId not in(select StudentId from ScoreList)

2.exist 子查询

use StudentManageDB
go
if exists(select * from ScoreList where CSharp<60)
   print '本次考试内容较难'
else
   print '本次考试内容适中'

--NOT EXISTS的使用
if not exists(select * from ScoreList where CSharp<60)
      print '本次考试内容适中'
else
      print '本次考试内容较难'