select 查询列表
from 表1 [连接类型] join 表2 
on 连接条件
where 筛选条件;

select 查询列表
from 表1 inner join 表2 
on 连接条件
[where 筛选条件];

SELECT
    e.last_name,
    d.department_name
FROM
    employees e
INNER JOIN departments d ON e.department_id = d.department_id;

SELECT
    e.last_name,
    j.job_title
FROM
    employees e
INNER JOIN jobs j ON e.job_id = j.job_id
WHERE
    e.last_name LIKE ‘%e%‘;

SELECT
    l.city,
    count(*) `count`
FROM
    departments d
INNER JOIN locations l ON d.location_id = l.location_id
GROUP BY
    l.city
HAVING
    `count` > 3;

SELECT
    d.department_name,
    count(*) 员工个数
FROM
    employees e
INNER JOIN departments d ON e.department_id = d.department_id
GROUP BY
    d.department_name
HAVING
    员工个数 > 3;

SELECT
    e.last_name 员工名,
    d.department_name 部门名,
    j.job_title 工种名
FROM
    employees e
INNER JOIN departments d
INNER JOIN jobs j ON e.department_id = d.department_id
AND e.job_id = j.job_id
ORDER BY
    部门名;