数据在本专栏的第一篇博客里
sql99标准的连接查询,左连接就很方便
8.1.查询编号>3的女神的男朋友信息,如果有则列出详细的信息,如果没有,则用null
填充
SELECT
be.id,
be.NAME,
bo.*
FROM
beauty be
LEFT JOIN boys bo ON be.boyfriend_id = bo.id
WHERE
be.id > 3;
8.2.查询哪个城市没有部门
SELECT
city,
department_name
FROM
locations l
LEFT JOIN departments d ON l.location_id = d.location_id
WHERE
department_name IS NULL;
8.3.查询部门名称为SAL
或IT
的员工信息
SELECT
e.*,
department_name
FROM
employees e
LEFT JOIN departments d ON e.department_id = d.department_id
WHERE
department_name IN ( 'SAL', 'IT' );