Oracle学习笔记2

一．Select
1）select * from tablename;
2）select salary*12 from tablename;  //对列运算
3）select sysdate from dual;                     //获取当前时间
4）select salary*12 annual_salary from tablename;        //为列起别名
//为列起区分大小写或着带空格的别名
select salary*12 “annual salary” from tablename;    
5）select ename || salary from emp;                 //连接两个列
6）select distinct deptno from emp;          //去掉重复的值
          Select distinct ename, job from emp;  //去掉ename，job都相同的记录
7）select * from emp where ename > ‘cba’;    //比较字符串条件，按ascii码
8）select * from emp where salary between 800 and 1500;  //between and 查询
9）//in查询
select * from emp where ename in (‘abc’, ‘def’);
select * from emp where salary not in (‘abc’, ‘def’);
10）              //空值比较
select * from emp where ename is null;
select * from emp where ename is not null;
11）              //%代表0或多个字符，_代表一个字符
select * from emp where ename like ‘_a%’;
select * from emp where ename like ‘abc/%’ escape ‘/’;              //定义转义字符
12）              select * from dept order by deptno desc/asc;                //order by排序
    &