MySQL查詢援助

Question

下面是表的說明，我使用：

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) 

---

下面是數據庫中的示例數據：

+------------+-----------+------------+---------+------------+ 
| 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) 

---

結果我試圖得到的是一個將類似於以下內容：

+------------+-----------+------------+---------+------------+------------+ 
| 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 | 
+------------+-----------+------------+---------+------------+------------+ 

• 倘若學生ID列是唯一的。
• 凡測驗列取決於有多少測驗是 原始表繼續。並且測驗欄包含各自的學生的每個 的等級。

Answer 1

試試這個：

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 

看到this