数据库之数据查询
1、–简单查询
use student_412
select Sid,Sname From Student_info where Sname = '陈文'
2、–查询所有
use student_412
select * from Student_info
3、–选择部分列并指定他们的显示次序
use student_412
select Sname,Sgender From Student_info
4、–更改列标题方式1
use student_412
select Sid '学号',Sname '姓名',Sgender '性别',Sdepart '系别' From Student_info
5、–更改列标题方式2
use student_412
select Sid as '学号',sname as '姓名',Sgender as '性别',Sdepart as '系别' From Student_info
6、–更改标题方式3
use student_412
select '学号'=Sid,'姓名'=Sname,'性别'=Sgender,'系别'=Sdepart From Student_info
7、–通用方式,使用getdate()函数获得当前系统时间
use student_412
select Sname '姓名',YEAR(GETDATE())-YEAR(Sbirth) '年龄' From Student_info
8、–获取被选修的课程编号,课程编号重复
use student_412
select Cid From SC
9、–删除重复行,使用distinct(获取被选修的课程编号),课程编号不重复
use student_412
select distinct Cid From SC
10、–返回限制的行数(从头数)
use student_412
select top 6 Sid From SC
11、–返回限制的行数(返回的行数等于总行数的百分之几)
use student_412
select top 42 percent Sid From SC