--查询列 Select t.sname,t.ssex,t.class from student t --t 别名; Select *from student t; --* 代表查询表内所有数据 Select *from student t where t.sclass='95031'; --规定判断条件t.sclass='95031'，用where连接 Select t.sname as 姓名,t.ssex 性别,t.class 班级 from student t where t.sclass='95031'; --将列名翻译成汉文 Select t.sname||t.ssex||t.class from student t where t.sclass='95031' or t.ssex='女'; --||代表将查询数据连接 --升降续查询 select * from STUDENT t order by sclass; --order by 升序排列， 默认的加上asc select * from STUDENT t order by sclass desc; --order by sclass desc 降序排列， select * from STUDENT t order by sclass desc,sno asc; --同时进行多个字段进行排序，先对sclass进行降序，在对sno升续排列 Select distinct t.depart t.prof from teacher t; --distinct使depart字段与Prof字段不重复列查询出来 --关系查询 Select * from student t where t.sno in (select e.sno from score e where degree between 60 and 80); --degree between 60 and 80在degree列，取在60到80之间成绩学生信息， Select * from student t where t.sno in (select e.sno from score e where degree in(85,86,88)); --degree in(85,86,88) 在degree列取85,86,88的成绩学生信息 --in() 子查询 --模糊查询 select * from STUDENT t where sname like '王%'; --查询STUDENT表中性王的人的信息，%代表任意数量 关键字like select * from STUDENT t where sname not like '王_'; --下划线_代表一个字符，查询姓王的两个字的名字， --限制返回记录条件 select * from score where rownum=1; --rownum=1 伪列，在列表中是隐藏的 select * from (select * from score order by degree desc) where rownum=1; --from后也可以加结果集，作为虚拟表 --分组查询 group by --按照课程编号分组，在计算每组平均值 select cno,avg(degree),count(1) from score t group by cno; --连接查询 --内连接查询 select Sname,cno,degree from score s,student t where t.sno=s.sno; --将两个表score，student表创建练习。 select Sname,cno,degree from score s join student t on t.sno=s.sno; --标准内连接格式 --外联接查询 select Sname,cno,degree from score s left join student t on t.sno=s.sno; --left join 左外联，将左侧表内数据对不上的信息查询出来， select Sname,cno,degree from score s left join student t on t.sno=s.sno; --right join右外联，将右侧表内数据对不上的信息查询出来， --全连接 select Sname,cno,degree from score s full join student t on t.sno=s.sno; --full join全连接，将左，右两侧表内数据的信息全部查询出来，