Question

我有4个名为student，address，phone和record的表，我可以使用第一列加入每个表。

学生

+----+-------------+
| id | studentName |
+----+-------------+
|  1 | Name_1      |
|  2 | Name_2      |
+----+-------------+

地址

+----+-------------+
| id | addressName |
+----+-------------+
|  1 | address_1   |
|  1 | address_2   |
|  2 | address_3   |
+----+-------------+

电话

+----+-------------+
| id | phoneNumber |
+----+-------------+
|  1 |      123456 |
|  2 |      987654 |
+----+-------------+

记录

+----+-----------+
| id | recNumber |
+----+-----------+
|  1 | REC001    |
|  2 | REC002    |
+----+-----------+

选择查询

select s.id,s.studentName,a.addressName,p.phoneNumber,r.recNumber
from student s
 join address a on  s.id=a.id
 join phone p on  s.id=p.id
 join  record r on s.id=r.id

这些表上的

给了我一个输出

+----+-------------+-------------+-------------+-----------+
| id | studentName | addressName | phoneNumber | recNumber |
+----+-------------+-------------+-------------+-----------+
|  1 | Name_1      | address_1   |      123456 | REC001    |
|  1 | Name_1      | address_2   |      123456 | REC001    |
|  2 | Name_2      | address_3   |      987654 | REC002    |
+----+-------------+-------------+-------------+-----------+

我想将其转换为类似

的内容

+----+-------------+-------------+-------------+-----------+-----------+
| id | studentName | addressName | phoneNumber | recNumber | flag      |
+----+-------------+-------------+-------------+-----------+-----------+
|  1 | Name_1      | address_1   | null        | null      | address   |
|  1 | Name_1      | address_2   | null        | null      | address   |
|  2 | Name_2      | address_3   | null        | null      | address   |
|  1 | Name_1      | null        | 123456      | null      | phone     |
|  2 | Name_2      | null        | 987654      | null      | phone     |
|  1 | Name_1      | null        | null        | REC001    | record    |
|  2 | Name_2      | null        | null        | REC002    | record    |
+----+-------------+-------------+-------------+-----------+-----------+

flag列中的值不必是表名，任何常量都可以。

我使用temptable（通过将整个细节添加到一个临时表中并通过使用flag重新插入数据）来完成它。有没有选择直接获得它？

带有上述数据的

rextester

Answer 1

您可以使用UNION执行此操作：

SELECT id, studentName, addressName, 
       NULL AS phoneNumber, NULL as recNumber, 'address' as flag
FROM student s
JOIN address a ON s.id = a.id

UNION

SELECT id, studentName, NULL, 
       phoneNumber, NULL, 'phone' as flag
FROM student s
JOIN phone p ON s.id = p.id

UNION

SELECT id, studentName, NULL, 
       NULL, recNumber, 'record' as flag
FROM student s
JOIN record r ON s.id = r.id

Answer 2

您应该能够在查询中使用CASE WHEN和LEFT OUTER JOIN获取额外的列

select s.id,s.studentName,a.addressName,p.phoneNumber,r.recNumber, 
CASE WHEN a.addressName IS NOT NULL THEN 'address'
WHEN p.phoneNumber IS NOT NULL THEN 'phone'
ELSE 'record' AS flag 
from student s
 LEFT OUTER join address a on  s.id=a.id
 LEFT OUTER join phone p on  s.id=p.id
 LEFT OUTER join  record r on s.id=r.id

创建动态列以标记选择查询中的现有数据

2 个答案: