版权声明:所有的博客都是个人笔记,交流可以留言。未经允许,谢绝转载。。。 https://blog.csdn.net/qq_35976351/article/details/88747580
题目描述
查找所有员工的last_name和first_name以及对应的dept_name,也包括暂时没有分配部门的员工
CREATE TABLE departments
(
dept_no
char(4) NOT NULL,
dept_name
varchar(40) NOT NULL,
PRIMARY KEY (dept_no
));
CREATE TABLE dept_emp
(
emp_no
int(11) NOT NULL,
dept_no
char(4) NOT NULL,
from_date
date NOT NULL,
to_date
date NOT NULL,
PRIMARY KEY (emp_no
,dept_no
));
CREATE TABLE employees
(
emp_no
int(11) NOT NULL,
birth_date
date NOT NULL,
first_name
varchar(14) NOT NULL,
last_name
varchar(16) NOT NULL,
gender
char(1) NOT NULL,
hire_date
date NOT NULL,
PRIMARY KEY (emp_no
));
解题思路
多个表的左连接
AC代码
SELECT last_name, first_name, dept_name FROM
(employees AS e LEFT JOIN dept_emp AS d ON (e.emp_no = d.emp_no)) AS tmp LEFT JOIN
departments d1 ON tmp.dept_no = d1.dept_no