使用具有关系的表获取一个表中的相关行

Question

我有两张桌子。一个存储内容记录，另一个存储内容记录之间的关系。

table "content"             table "relations"  
+---+-----+------+------+   +---------+----------+  
|id |num  |text  |value |   |id_local |id_foreign|  
+---+-----+------+------+   +---------+----------+  
|1  |111  |aaa   |12345 |   |2        |3         |  
+---+-----+------+------+   +---------+----------+  
|2  |222  |bbb   |23456 |   |2        |5         |  
+---+-----+------+------+   +---------+----------+  
|3  |333  |ccc   |34567 |   |4        |1         |  
+---+-----+------+------+   +---------+----------+  
|4  |444  |ddd   |45678 |   |2        |1         |  
+---+-----+------+------+   +---------+----------+  
|5  |555  |eee   |56789 |   |3        |6         |  
+---+-----+------+------+   +---------+----------+  
|6  |666  |fff   |67890 |   |4        |5         |  
+---+-----+------+------+   +---------+----------+  

阅读表“关系”

id_local = 内容中记录的 ID（“父级”）
id_foreign = 与 id_local（“child”）相关的内容中记录的 id

我希望 content.num = 222 的所有关系按照它们在表“关系”中输入的顺序。结果应如下所示：

result  
+-----+------+  
|num  |value |  
+-----+------+  
|333  |34567 |  
+-----+------+  
|555  |56789 |  
+-----+------+  
|111  |12345 |  
+-----+------+  

我尝试了一些 JOIN，但从未得到这个结果。

请问，有人知道我怎样才能得到这个结果吗？

其他问题：

如果我想输出带有所有“子”记录的“父”记录的 content.value=23456，查询应该是什么样子？

result 2
+-----+------+--------+  
|num  |value | p-value|  
+-----+------+--------+
|333  |34567 | 23456  |  
+-----+------+--------+  
|555  |56789 | 23456  |    
+-----+------+--------+  
|111  |12345 | 23456  |  
+-----+------+--------+  

Answer 1

我猜这是一种奇怪的方法，但是；

SELECT num, value
FROM content
WHERE id IN (
  SELECT id_foreign
  FROM relations
  WHERE id_local = ( SELECT id FROM content WHERE num = '222' )
  )
  AND num = '222' -- Additional answer

Answer 2

select  c2.num
,       c2.value
from    content c1
join    relations r
on      c1.id = r.id_local
join    content c2
on      r.id_foreign = c2.id
where   c1.num = 222

Example at SQL Fiddle.

Answer 3

我认为这里不需要join。

您只需要“父”记录的 ID。在本例中为 2。

Select num, value from content where id in (select id_foreign where id_local=2)

如果您不知道 ID，而只知道 num 值...

Select num, value from content where id in (select id_foreign where id_local=(select id from content where num='222'))