mysql：一对多给自己加入

Question

我有这张桌子：

id   name     parent_id
0    fruit    NULL
1    place    NULL
2    apple    0
3    orange   0
4    beach    1
5    forest   1

我希望得到这样的结果：

id   name    name
0    fruit   NULL
1    place   NULL
2    apple   fruit
3    orange  fruit
4    beach   place
5    forest  place

我试过这个：

SELECT * FROM foobar LEFT OUTER JOIN foobar c ON c.parent_id = c.id

但它不起作用。

Answer 1

在JOIN c加入c 本身。您必须加入foobar加入SELECT foobar.id, foobar.name, c.name FROM foobar LEFT OUTER JOIN foobar c ON foobar.parent_id = c.id 。试试这个：

{{1}}

Answer 2

SELECT c.id, c.name, a.name as [parent] FROM foobar a LEFT OUTER JOIN foobar c ON c.parent_id = a.id