使用外键关系的MySQL查询
我正在学习MySQL,我正在尝试在查询中做简单的算法, 我正在尝试编写一个命令,以确定大学各学院的使用外键关系的MySQL查询,mysql,Mysql,我正在学习MySQL,我正在尝试在查询中做简单的算法, 我正在尝试编写一个命令,以确定大学各学院的讲师人数 有人能帮我吗?谢谢大家! 以下是我的两张桌子: ________________________________________________________ | Department | Faculty | Building | ---------------------------------------
讲师人数
有人能帮我吗?谢谢大家!
以下是我的两张桌子:
________________________________________________________
| Department | Faculty | Building |
--------------------------------------------------------
| Humanities | Arts and Sciences | Chardon |
| English | Arts and Sciences | Chardon |
| Mathematics | Arts and Sciences | Monzon |
| General Engineering | Engineering | Stefani |
| Agronomy | Agriculture | Pinero |
_________________________________________________________________________
| Professor | Department | Rank | Salary |
---------------------------------------------------------------------------
| Joe Blow | Biology | Professor | $73,500.00 |
| Sam Snow | Mathematics | Instructor | $45,700.00 |
| George Grow | Electrical Engineering | Associate Professor | $69,250.00 |
| Hiram Lowe | English | Assistant Professor | $63,750.00 |
与此相近的是:
select department.faculty, count(professor.professor) as instructors from department join professor on department.department = professor.department group by department.faculty
基本上,您可以通过联接“合并”两个表,然后按教员对结果进行分组,并计算每个教员的教授人数。类似于此:
select department.faculty, count(professor.professor) as instructors from department join professor on department.department = professor.department group by department.faculty
基本上你做一个连接来“合并”两个表,然后按教员对结果进行分组,并计算每个教员的教授数