（三）Oracle学习笔记—— sql语句

0. scott 用户默认表介绍

scott用户Tables目录下包含四张表

1. insert（插入）语句

给指定列插入数据：

insert into dept(deptno,dname) values(50,'xx');

插入全部列数据：

insert into dept(deptno,dname,loc) values(60,'xx','lll');

2. update（更新）语句

update dept set dname='司法部' where deptno=50;
update dept set dname='司法部' ,loc='china' where deptno=50;

3. delete（删除）语句

删除指定数据：

delete from dept where deptno=70;

删除指定条件的数据：

delete from dept where deptno>40;

4. select（查询）语句

查询所有：

select * from emp;

指定字段查询：

select ename,sal from emp;

简写 

insert into dept values(70,'xxx','llll');

加 where 条件：

select * from emp where sal>=800;
select * from emp where sal>=1500 and job='SALESMAN';

Distinct 去重复记录；

Group by 分组查询：select job,count(ename) as num from EMP t group by job;

Having 过滤分组：select job,count(ename) as num from EMP t group by job having count(ename)>=2;

Order by 排序：select * from emp order by sal desc;

子查询：查询出基本工资大于平均工资的员工：select * from emp where sal>(select avg(sal) from emp)

联合查询：

并集（去重复）：

select * from t_user1
union
select * from t_user2;

并集：

select * from t_user1
union all
select * from t_user2;

交集：

select * from t_user1
intersect
select * from t_user2;

差集：

select * from t_user1
minus
select * from t_user2;

内连接：

select * from emp t,dept d where t.deptno=d.deptno;

类似：select * from emp e inner join dept d on e.deptno=d.deptno; inner 可以省略；

外连接：

左外连接：select * from emp e left join dept d on e.deptno=d.deptno;

右外连接：select * from emp e right join dept d on e.deptno=d.deptno;