mysql-2-where

#进阶2：条件查询
/*
语法：
SELECT 查询列表
FROM 表名
WHERE 筛选条件

分类：
1、按条件表达式筛选：>  <  =  !=  <>  >=  <=
2、按逻辑表达式筛选：&&  ||  ！  AND  OR  NOT
3、模糊查询：LIKE,  BETWEEN AND,  IN,  IS NULL
*/

USE myemployees;


#1、按条件表达式筛选
#案例1：查询工资大于12000的员工信息
SELECT * 
FROM employees
WHERE salary > 12000;


#2、按逻辑表达式筛选
#案例2：工资在10000到20000之间的员工名、工资以及奖金
SELECT Concat(last_name, ' ', first_name) AS "name",
	   salary,
       commission_pct
FROM employees
WHERE salary >= 10000 AND salary <= 20000;


#3、模糊查询
#案例3：查询员工名中包含字符a的员工信息
# % 通配符，任意多个任意字符
# _ 通配符，单个任意字符
SELECT *
FROM employees
WHERE last_name LIKE '%a%'; 

SELECT last_name, salary
FROM employees
WHERE last_name LIKE '__n_l%'; 

#案例4：查询员工名中第二个字符为_的员工名
#转义：\\
SELECT last_name
FROM employees
WHERE last_name LIKE '_\\_%'; 

#回顾案例2：工资在10000到20000之间的员工名、工资以及奖金
SELECT Concat(last_name, ' ', first_name) AS "name",
	   salary,
       commission_pct
FROM employees
WHERE salary BETWEEN 10000 AND 20000;

#案例5：查询员工的工种名
#IN的类型要相同
SELECT job_id 
FROM employees
WHERE job_id IN ('IT_PROG', 'AD_VP', 'AD_PRES');

#案例6：没有奖金的员工
#IS NOT NULL,  IS NULL
SELECT last_name, commission_pct
FROM employees
WHERE commission_pct IS NULL;

#安全等于 <=>，本质就是等于
#可读性略低
SELECT last_name, commission_pct
FROM employees
WHERE commission_pct <=> NULL;

SELECT last_name, salary
FROM employees
WHERE salary <=> 12000;