Mysql基础语法

select查询

#查询信息   SELECT...FROM...;
SELECT * FROM employees;

SELECT employee_id,last_name,salary
FROM employees;

#重命名  ...AS...  或 " "
SELECT employee_id emd_id,last_name AS lname,department_id "部门id",salary * 12 AS "annual sal"
FROM employees;

#去重 DIDTINCT
SELECT DISTINCT department_id
FROM employees;

SELECT DISTINCT department_id,salary
FROM employees;

#替换NULL  INNULL(... , ...)
SELECT employee_id,salary AS "月工资",salary * (1 + IFNULL(commission_pct,0)) *12 AS "年工资"
FROM employees;

#着重号  ` ` 替换mysql中与关键字重名的表名
SELECT * FROM `order`;

#查询常数
SELECT '尚硅谷',employee_id,last_name
FROM employees;

#显示表结构，字段的详细信息
DESCRIBE employees;

#过滤数据
SELECT *
FROM employees
WHERE department_id = 90;

# 运算符 +、-、*、/、%
SELECT 100 + 2, 100 - 2, 100 * 2, 100 / 2, 100 % 2
FROM DUAL;