mySQL连接查询(多表查询)---等值连接（基于99版）

#查询员工名和他所在部门的部门名

SELECT e.last_name 员工名, d.department_name 部门名 #92版本
FROM
	employees e, departments d
WHERE 
	e.`department_id` = d.`department_id`;

SELECT e.last_name 员工名, d.department_name 部门名 #99版
FROM 
	employees e
INNER JOIN
	`departments` d
ON
	e.`department_id` = d.`department_id`;

#查询员工名字中包含字母‘e’的员工和其所在的部门

SELECT e.last_name 员工名, d.department_name 部门名
FROM 
	employees e
INNER JOIN 
	departments d
ON
	e.`department_id` = d.`department_id`
WHERE
	e.`last_name` LIKE '%e%';

输出：

#查询部门数大于0的城市的城市名和该城市的部门个数

SELECT l.city 城市名, COUNT(*) 部门个数
FROM
	locations l
INNER JOIN
	departments d
ON
	d.`location_id` = l.`location_id`
GROUP BY
	l.`city`#d.`location_id`#
HAVING
	COUNT(*) >0 ;

输出结果：