sql99的非等值连接和自连接

#(2)非等值连接

#查询员工的工资级别

SELECT salary,grade_level

FROM employees e

JOIN job_grades g

ON e.salary BETWEEN g.lowest_sal AND g.highest_sal;

#查询每个工资级别的个数>20的个数，并且按工资级别降序

SELECT COUNT(*),grade_level

FROM employees e

JOIN job_grades g

ON e.salary BETWEEN g.lowest_sal AND g.highest_sal

GROUP BY grade_level

HAVING COUNT(*)>20

ORDER BY grade_level DESC;

#(3)自连接

#查询姓名中包含字符k的员工的名字、上级的名字

SELECT e.last_name,m.last_name

FROM employees e

JOIN employees m

ON e.`manager_id`=m.`employee_id`

WHERE e.`last_name` LIKE '%k%';