– 34. 查询所有员工的姓名和部门名称，没有部门的员工不需要展示

SELECT
	e.NAME '员工姓名',
	d.NAME '部门名称' 
FROM
	t_emp e
	INNER JOIN t_dept d ON e.dept_id = d.id;

– 35. 查询所有员工的姓名和部门名称，没有部门的员工展示BOSS

SELECT
	e.NAME '员工姓名',
	ifnull( d.NAME, 'BOSS' ) '部门名称' 
FROM
	t_emp e
	LEFT JOIN t_dept d ON e.dept_id = d.id;

– 36. 查询jones所在部门的部门名称

SELECT
	e.NAME '员工姓名',
	d.NAME '部门名称' 
FROM
	t_emp e
	INNER JOIN t_dept d ON e.dept_id = d.id 
WHERE
	e.NAME = 'jones';

– 37. 找出谁是领导

SELECT DISTINCT
	e.NAME '员工姓名' 
FROM
	t_emp e
	INNER JOIN t_emp e2 ON e.id = e2.manager_id;

– 38. 找出谁不是领导

SELECT
	`name` 
FROM
	t_emp e 
WHERE
	NOT EXISTS ( SELECT 1 FROM t_emp e2 WHERE e2.manager_id = e.id );

– 39. 找出那些部门没有员工

SELECT
	d.NAME 
FROM
	t_dept d
	LEFT JOIN t_emp e ON e.dept_id = d.id 
WHERE
	e.id IS NULL;

– 40. 找出那些部门有员工

SELECT DISTINCT
	d.NAME 
FROM
	t_dept d
	LEFT JOIN t_emp e ON e.dept_id = d.id 
WHERE
	e.id IS NOT NULL;

– 41. 找出所有工资比martin高的员工

SELECT
	e1.NAME,
	e1.salary 
FROM
	t_emp e1,
	t_emp e2 
WHERE
	e1.salary > e2.salary 
	AND e2.NAME = 'martin' 
	AND e1.dept_id IS NOT NULL;