T-SQL 简单子查询

1.使用变量的方式实现的查询

 use StudentManageDB
 go
 declare @StuId int
 --查询张永利学号
 select @StuId=StudentId from Students where StudentName='张永利'
 --查询学号排在张永利后面的学员
 select StudentId,StudentName,Gender,Birthday from Students
 where StudentId>@StuId

2.简单子查询

 use StudentManageDB
 go

 --查询学号排在张永利后面的学员
 select StudentId,StudentName,Gender,Birthday from Students
 where StudentId>(select StudentId from Students where StudentName='张永利')

3.连表查询

 use StudentManageDB
 go
 --使用等值连接查询
 select StudentName from Students
 inner join ScoreList on Students.StudentId=ScoreList.StudentId
 where SQLServerDB>90

 select StudentId,StudentName from Students
 select StudentId,SQLServerDB from ScoreList

4.使用连表查询替换子查询

 use StudentManageDB
 go
 --使用子查询
 select StudentName from Students
 where StudentId=(select StudentId from ScoreList where SQLServerDB>90)