mysql之条件查询

语法：
	select 
		查询列表
	from
		表名
	where
		筛选条件;

简单条件运算符：> < = != <> >= <=

逻辑运算符：
	作用：用于连接条件表达式
		&& || !
		and or not
		
	&&和and：两个条件都为true，结果为true，反之为false
	||或or： 只要有一个条件为true，结果为true，反之为false
	!或not： 如果连接的条件本身为false，结果为true，反之为false

like
between and
in
is null

SELECT 
	*
FROM
	employees
WHERE
	salary>12000;

SELECT 
	last_name,
	department_id
FROM
	employees
WHERE
	department_id<>90;

SELECT
	last_name,
	salary,
	commission_pct
FROM
	employees
WHERE
	salary>=10000 AND salary<=20000;

SELECT
	*
FROM
	employees
WHERE
	# department_id<90 OR department_id>110 OR salary>15000;
	NOT(department_id>=90 AND  department_id<=110) OR salary>15000;

like	
between and
in
is null|is not null

特点：
1.一般和通配符搭配使用
通配符：
	% ：任意多个字符,包含0个字符
	_ ：任意单个字符

select 
	*
from
	employees
where
	last_name like '%a%';	#abc

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

SELECT
	last_name
FROM
	employees
WHERE
	last_name LIKE '_$_%' ESCAPE '$';

where last_name LIKE '_\_%';

SELECT
	*
FROM
	employees
WHERE
	employee_id >= 100 AND employee_id<=120;

SELECT
	*
FROM
	employees
WHERE
	employee_id BETWEEN 100 AND 120;

SELECT
	last_name,
	job_id
FROM
	employees
WHERE
	job_id = 'IT_PROT' OR job_id = 'AD_VP' OR JOB_ID ='AD_PRES';

SELECT
	last_name,
	job_id
FROM
	employees
WHERE
	job_id IN( 'IT_PROT' ,'AD_VP','AD_PRES');

SELECT
	last_name,
	commission_pct
FROM
	employees
WHERE
	commission_pct IS NULL;

SELECT
	last_name,
	commission_pct
FROM
	employees
WHERE
	commission_pct IS NOT NULL;

SELECT
	last_name,
	commission_pct
FROM
	employees

WHERE 
	salary IS 12000;

SELECT
	last_name,
	commission_pct
FROM
	employees
WHERE
	commission_pct <=>NULL;

WHERE
	commission_pct is NULL;

SELECT
	last_name,
	salary
FROM
	employees

WHERE 
	salary <=> 12000;