mysql数据库中select 基本查询（1）

mysql数据库中select 基本查询（1）

SELECT 1+'a'

FROM DUAL;

SELECT * FROM employees;

#mysql 基本运算

SELECT 1+1,3*2

FROM DUAL; #伪表

SELECT * FROM employees;

#查询员工的id,名字，薪资

SELECT employee_id,last_name,salary

FROM employees

#查询出有多少个部门，且不重复

SELECT DISTINCT department_id

FROM  employees;

SELECT salary,DISTINCT department_id

FROM employees;

SELECT DISTINCT salary, department_id

FROM employees;

#只要有null 的值参与运算的结果是null,所以查询出来的结果不准确

SELECT employee_id,salary "月工资",salary * (1 + commission_pct) * 12 "年工资",commission_pct

FROM employees

#改进方法 IFNULL(commission_pct,0) ,如果commission的值为null 则置为0

SELECT employee_id,salary "月工资",salary * (1 + IFNULL(commission_pct,0)) * 12 "年工资",commission_pct

FROM employees

# select * from order 错误的，因为order 是关键字 所以要用着重号

SELECT *FROM  `order`;

#查询90号部门员工的信息

DESC employees;

SELECT * FROM employees

WHERE department_id=90;

# 查询lastname 为king 的员工信息

SELECT employee_id,last_name,department_id

FROM employees

WHERE last_name='king';

#因为此处的sql语句 执行过程是 先执行from 子句，然后执行where 子句，最后执行select子句，

#所以会报Unknown column 'did' in 'where clause'

SELECT employee_id emid,last_name "姓名",department_id AS did

FROM employees

WHERE did=90;

SELECT employee_id emid,last_name "姓名",department_id AS 部门ID

FROM employees

WHERE department_id=90;

版权声明：本文内容由网络用户投稿，版权归原作者所有，本站不拥有其著作权，亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容，请联系我们jiasou666@gmail.com 处理，核实后本网站将在24小时内删除侵权内容。