php – 比较表中的mysql数据

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,我想将第一学期的学分与第二学期进行比较.即数学正在提高,英语水平正在下降

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

我只是取结果但不知道如何解决.任何帮助将不胜感激

解决方法:

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