如何从表的单行中获取多行？

Question

嗨，我有两个具有以下结构的表

学生们

 +------+------+------+-------+------+------+
| Col1 | Col2 | Col3 | Col4  | Col5 | Col6 |
+------+------+------+-------+------+------+
|   01 | Hari | 20   |    80 |   21 |   81 |
|   02 | Nari | 20   |    67 |   21 |   76 |
|   02 | Lari | 25   |    87 |   26 |   96 |
+------+------+------+-------+------+------+

此处COl1 = ID，Col2 =名称，Col3 = SubjectCode，COl4 = Col3中的标记，Col5 = subjectCpde，Col6 = Col5的标记

还有另一个表叫做Subjects

+------+-----------+
| Col1 |   Col2    |
+------+-----------+
|   20 | English   |
|   21 | Maths     |
|   25 | Chemistry |
|   26 | Physics   |
+------+-----------+

这里Col1 =学科代码，COl2 =在学生表中引用的学科名称。

现在，我的查询应按以下方式返回结果。 如何实现的？

+---------+--------+------+
| Subject |  Marks | Name |
+---------+--------+------+
| English |     80 | Hari |
| Maths   |     81 | Hari |
+---------+--------+------+

Answer 1

你可以试试看

使用两个查询，第一个查询English subjectCode ，第二个查询English subjectCode 。 然后使用UNION ALL组合它们。

SELECT sub.Col2 as 'Subject',stu.Col4 as 'Marks',stu.Col2 as 'Name'
FROM Students stu
inner join subjects sub on sub.Col1 = stu.Col3
WHERE stu.Col2 = 'Hari'
UNION ALL 
SELECT sub.Col2 as 'Subject',stu.Col6 as 'Marks',stu.Col2 as 'Name'
FROM Students stu
inner join subjects sub on sub.Col1 = stu.Col5
WHERE stu.Col2 = 'Hari'

http://sqlfiddle.com/#!9/513fe5/17