测试派 Give testers a home.

1、查询张姓员工的员工信息和所在部门信息。

SELECT * FROM emp a LEFT JOIN dept b ON a.dept_id = b.id WHERE a.name LIKE '张%'

2、查询张三丰管理了几个员工

SELECT count(b.id) FROM emp a INNER JOIN emp b ON a.id = b.leader WHERE a.name = '张三丰'

3、查询出所有实习员工（实习员工无部门信息）

SELECT * FROM emp a LEFT JOIN dept b ON a.dept_id = b.id where b.id IS NULL