确定过程

Question

我的数据如下

Schedule
+------------+----------------+
|   Date     | Lesson Teacher |
+------------+----------------+
| 2018-01-03 | Math           |
| 2018-01-03 | English        |
| 2018-01-03 | Sports         |
| 2018-01-03 | Biology        |
| 2018-01-03 | Math           |
| 2018-01-03 | English        |
| 2018-01-03 | Sports         |
| 2018-01-03 | Biology        |
| 2018-01-04 | Math           |
| 2018-01-04 | English        |
| 2018-01-04 | Sports         |
| 2018-01-04 | Biology        |
+------------+----------------+

Teacher
+-------------+------------+-----------+
|   Lesson    |  Teacher   |  Priority |
+-------------+------------+-----------+
| Math        | Alex       |         1 |
| Math        | Bob        |         2 |
| Math        | Steve      |         3 |
| English     | Alex       |         1 |
| English     | Bertha     |         2 |
| Sports      | Noah       |         1 |
| Sports      | Steve      |         2 |
| Biology     | Bertha     |         1 |
| Biology     | Bob        |         2 |
+-------------+------------+-----------+

每位教师只能在一个日期教授1节课，所以如果时间表已经填满了第一优先级教师，那么下一课将在课程安排的同一日期填写第二课。有人可以帮忙吗？

THX

Answer 1

我会使用windows函数

select sch.date, sch.lesson, t.teacher
from teacher t
join 
(
   select s.*,
        row_number() over (partition by date, lesson order by date) priority
   from schedule s
) sch on sch.lesson = t.lesson and t.priority = sch.priority

demo