php - 比较表内的mysql数据

Question

我有一个 mysql 表 tbl_exam

user_ID | User_name | semester | math | english |
1       | John      | 1st      | 67   |  73     |
1       | John      | 2nd      | 82   |  59     |

在此之后，我想比较第一学期和第二学期的成绩。即数学在提高，英语在下降

user_ID | User_name | math  | english  |
1       | John      | good  | bad      |

我只是获取结果但不知道如何解决。任何帮助将不胜感激

Answer 1

试试这个:

SELECT A.user_id, A.user_name, IF((B.math - A.math) > 0, 'good', 'bad') math, 
         IF((B.english - A.english) > 0, 'good', 'bad') english
FROM (SELECT user_id, user_name, math, english 
FROM tbl_exam WHERE semester = '1st') AS A 
INNER JOIN 
(SELECT user_id, user_name, math, english 
FROM tbl_exam WHERE semester = '2nd') AS B ON A.user_id = B.user_id