oracle（表的查询1）

查询表结构

desc dept;

查询所有列

select *from dept;

查询指定列

select deptno, job from emp;

过滤重复的内容

select distinct deptno, job from emp;

按条件查询

select sal, job, deptno, ename from emp where ename='SMITH';

select *from emp where hiredate>'1981-1-1';

表达式， 空值，别名 nvl

select sal, sal*12+nvl(comm, 0) as "年薪", ename, job from emp;

连接查询

select ename || ' is a ' || job from emp;   //SMITH is a CLERK

多条件查询

select sal, ename from emp where sal>=2000 and sal < 3000;

排序 升序

select *from emp order by hiredate;

排序 降序

select *from emp order by hiredate desc;

使用like操作符  (%表示0到任意个字符， _表示单个字符)

select ename, sal from emp where ename like '%S%';

select ename, sal from emp where ename like '_O%';

在where中使用in

select *from emp where deptno in(10, 20);

select *from emp where deptno in(10, 20) order by deptno, sal;

查询空

select *from emp where mgr is null;