MySQL可以按column1进行排序，也可以按column2进行排序

Question

假设我有2张桌子，courses和books

课程

| id | name         | is_sort_by_borrower |
|----|--------------|---------------------|
| 1  | Comp Science | 1                   |
| 2  | Biz Admin    | 0                   |
| 3  | Physics      | 1                   |

[books

| id  | title  | borrower | last_borrow_date | course_id |
| --- | ------ | -------- | ---------------- | --------- |
| 1   | Book A | 523      | 11/12/19 12:33   | 1         |
| 2   | Book B | 423      | 11/15/19 12:33   | 1         |
| 3   | Book C | 401      | 10/22/19 12:33   | 1         |

[课程中有一列is_sort_by_borrower，我想得到这样的结果

| course       | book_title | borrower | last_borrow_date | is_sort_by_borrower |
|--------------|------------|----------|------------------|---------------------|
| Comp Science | Book A     | 523      | 11/12/19 12:33   | 1                   |
| Comp Science | Book B     | 423      | 11/15/19 12:33   | 1                   |
| Comp Science | Book C     | 401      | 10/22/19 12:33   | 1                   |
| Comp Science | Book D     | 377      | 11/19/19 12:33   | 1                   |
| Biz Admin    | Book E     | 122      | 11/20/19 12:33   | 0                   |
| Biz Admin    | Book F     | 419      | 11/12/19 12:33   | 0                   |
| Biz Admin    | Book G     | 65       | 10/18/19 12:33   | 0                   |
| Physics      | Book H     | 446      | 8/31/19 12:33    | 1                   |
| Physics      | Book I     | 398      | 11/2/19 12:33    | 1                   |
| Physics      | Book J     | 376      | 9/30/19 12:33    | 1                   |
| Physics      | Book K     | 249      | 10/11/19 12:33   | 1                   |

是否可以按borrower排序结果，按last_borrow_date排序结果？

Answer 1

是，在SELECT中创建另一列，并使用CASE向其中填充所需的值，然后按此排序。您还可以在WHERE子句中使用CASE语句，具体取决于您是否希望排序列显示结果。

ref：MYSQL ORDER BY CASE Issue

ref：https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html

在您的示例中：

SELECT
    c.id, c.name, c.is_sort_by_borrower, 
    b.id, b.title, b.borrower, b.last_borrow_date
FROM
    courses c
INNER JOIN
    books b on b.course_id = c.id
ORDER BY
    CASE 
        WHEN is_sort_by_borrower=1 THEN borrower
        WHEN is_sort_by_borrower=0 THEN last_borrow_date 
    END ASC