这是我正在使用的表的描述:
describe mjla_db.StudentRecordTable2;
+-----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| classId | varchar(20) | NO | MUL | NULL | |
| studentId | varchar(20) | NO | MUL | NULL | |
| quizGrade | tinyint(4) | YES | | NULL | |
| quizId | int(11) | NO | MUL | NULL | |
+-----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
这是数据库中的示例数据:
+------------+-----------+------------+---------+------------+
| Student ID | Last Name | First Name | Quiz ID | Quiz Grade |
+------------+-----------+------------+---------+------------+
| A1 | Cat | Tom | 19 | 75 |
| A2 | pancake | Harry | 19 | 65 |
| A5 | Worthy | Dick | 19 | NULL |
| A1 | Cat | Tom | 20 | 55 |
| A2 | pancake | Harry | 21 | NULL |
| A2 | pancake | Harry | 20 | 47 |
| A5 | Worthy | Dick | 20 | 95 |
| A1 | Cat | Tom | 21 | 55 |
| A5 | Worthy | Dick | 21 | 95 |
+------------+-----------+------------+---------+------------+
3 rows in set (0.00 sec)
我试图获得的结果类似于以下内容:
+------------+-----------+------------+---------+------------+------------+
| Student ID | Last Name | First Name | Quiz 19 | Quiz 20 | Quiz 21 |
+------------+-----------+------------+---------+------------+------------+
| A1 | Cat | Tom | 75 | 55 | 55 |
| A2 | pancake | Harry | 65 | 47 | NULL |
| A5 | Worthy | Dick | NULL| 95 | 95 |
+------------+-----------+------------+---------+------------+------------+
- 学生 ID 列是唯一的。
- 测验列的继续位置取决于测验的数量 原来的表。测验列包含每个人的成绩 各自的学生。
最佳答案
试试这个:
select s.StudentId, s.FirstName, s.LastName,
Case when s.QuizId = 19 then quizGrade end as 'Quiz 19',
Case when s.QuizId = 20 then quizGrade end as 'Quiz 20',
Case when s.QuizId = 21 then quizGrade end as 'Quiz 21'
from StudentRecordTable2 sr
inner join Students s on sr.StudentId = s.StudentId
参见 this
关于MySQL查询协助，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7863791/