MySQL11 - 多表连接

多表连接

语法：

SELECT
	...
FROM
	A 
	(INNER) JOIN B ON A-B连接条件
	(RIGHT) JOIN C ON A-C连接条件
	(LEFT) JOIN D ON A-D连接条件

例子：找出每个员工的部门名称、工资等级以及上级领导，要求显示员工名、领导名、部门名、薪资、薪资等级

SELECT
	a.ename AS WORKER,b.ename AS BOSS, a.sal, d.dname, s.grade
FROM
	emp a
LEFT JOIN
	emp b
ON
	a.MGR = b.empno
JOIN
	dept d
ON
	a.deptno = d.deptno
JOIN
	salgrade s
ON
	a.sal BETWEEN s.losal AND s.hisal
ORDER BY
	a.sal ASC;