select count from multiple tables（多表计数查询）

今天在实验楼上面学习sql语句，觉得好有成就感。卡在作业题目上面卡了好久。
题目是这样：

使用连接查询的方式，查询出**各员工所在部门的人数与工程数**，工程数命名为count_project。（连接3个表，并使用COUNT内置函数）

做了很多尝试，列出表的内容等等。
具体尝试内容可以查看这里：https://www.shiyanlou.com/courses/reports/549775
最终在网上找到了答案：http://goobbe.com/questions/5113072/mysql-multiple-count-from-multiple-tables-with-left-join
撒花！做出来了好开心！

sql语句如下：

SELECT department.dpt_name, 
COUNT(DISTINCT project.proj_name) AS 'count_project',
COUNT(DISTINCT employee.name) AS 'count_people'
FROM department
LEFT JOIN project
ON project.of_dpt=department.dpt_name
LEFT JOIN employee
ON employee.in_dpt=department.dpt_name
GROUP BY department.dpt_name;

显示的结果：

mysql> SELECT department.dpt_name, 
    -> COUNT(DISTINCT project.proj_name) AS 'count_project',
    -> COUNT(DISTINCT employee.name) AS 'count_people'
    -> FROM department
    -> LEFT JOIN project
    -> ON project.of_dpt=department.dpt_name
    -> LEFT JOIN employee
    -> ON employee.in_dpt=department.dpt_name
    -> GROUP BY department.dpt_name
    -> ;
+----------+---------------+--------------+
| dpt_name | count_project | count_people |
+----------+---------------+--------------+
| dpt1     |             1 |            3 |
| dpt2     |             2 |            4 |
| dpt3     |             1 |            3 |
| dpt4     |             2 |            2 |
+----------+---------------+--------------+
4 rows in set (0.00 sec)

继续加油咯！