mysql数据库中的优化mysql查询

Question

我想从仅属于类rows最后一行的class表中获取3个5,6 and 7数据。

现在，我正在使用3个sql查询来获取数据：

 1. SELECT * from class where class_name = '5';

 2. SELECT * from class where class_name = '6';

 3. SELECT * from class where class_name = '7';

如何使用单个sql查询来检索3行数据而不是3次sql查询？

**class table structure:**

|id | class_name | student  |
|---| -----------| ---------| 
|1  |      5     | Student A|
|2  |      6     | Student B|
|3  |      4     | Student C|
|4  |      6     | Student D|
|5  |      7     | Student E|
|6  |      5     | Student F|
|7  |      4     | Student G|
|8  |      6     | Student H|
|9  |      5     | Student I|
|10 |      6     | Student J|
|11 |      7     | Student K|
|12 |      6     | Student L|
|13 |      8     | Student M|
|14 |      6     | Student N|
|15 |      8     | Student O|

成绩要求：学生I，学生N和学生K

Answer 1

尝尝这个

SELECT * FROM class WHERE id IN (SELECT MAX(id) FROM class WHERE class_name in (5,6,7) GROUP BY class_name );

木琴

Answer 2

select * from (select * from class order by id desc, class_name) x group by class_name

Answer 3

SELECT * from (SELECT * from class ORDER BY id  DESC) t WHERE class_name in (5,6,7) GROUP BY class_name ORDER BY id DESC