常用sql操作

sqlplus sys/sys as sysdba;
alert user scott account unlock;
desc emp;
select ename,sal*12 from emp;

select sysdate from dual; --dual为空表

select ename,sal*12 annual_sal from emp; --别名
--数值+null 为null
select ename||sal from emp; --拼串
select ename || 'aaa''bbb' from emp; --含'的拼串,''替换为'
select distinct deptno,job from emp; --去掉2个字段值的组合

select * from emp where deptno=10 and ename='CLARK';
select ename,sal from emp where sal >1500;
select ename,sal from emp where deptno <>10;
select ename,sal from emp where sal between 800 and 1500; -- sal>=800 and sal<=1500
select ename,sal,comm from emp where comm is null; --is not null
select ename,sal,comm from emp where sal in (800,1500); -- not in (800,1500)

select ename from emp where ename like '_A%' -- %为0个或多个，-为1个
select ename from emp where ename like '%\%%' -- 名字含有%，需要\为转义字符处理
select ename from emp where ename like '%$%%' escape '$'  -- 可以使用$作为转义字符

select ename,sal,deptno from emp order by deptno asc,ename desc;  -- 升序asc，降序 desc