sql语句基础

摘要: sql select sql plus

Select * from employees;

显示表的列:Desc employees

查看指定列:select department_id,location_id from employees;

算术运算符:

Select last_name,salary * 12 + 1000 from employees;

Select sysdate + 1 , sysdate , sydate – 1 from dual;(日期可以加减 不能乘除)

Txt下编辑：Ed(edit) /进行运行

凡是空值(null)参与的运算，结果都为空

别名Select employee_id id,last_name name,salary*12 total from employees;或者employee_id as id

双引号 Select employee_id “id”,last_name name,salary*12 total from employees;

连接符：把列与列，列与字符连接在一起 用||表示

Select last_name||’`s job _id is ‘||job_id from employees

“”用在别名

Select distinct department_id from employees;去重

Desc(describe) 是 sql plus关键字 描述表的结构