Question

我有下表taxonomy，如下所示：

taxonomy_id  | parent_id
------------------------
1            | 0
2            | 0
3            | 1
4            | 1
5            | 2
6            | 3

我想选择所有不是父母的物品，在4,5和6的情况下。前3项显然是父母，我不需要它们。应该是什么查询

Answer 1

使用NOT EXISTS

SELECT taxonomy_id, parent_id
FROM dbo.Taxonomy t1
WHERE NOT EXISTS(
    SELECT 1 FROM dbo.Taxonomy t2
    WHERE t1.taxonomy_id=t2.parent_id
)

Demonstration

至少在SQL-Server中，这是最好的方法： Should I use NOT IN, OUTER APPLY, LEFT OUTER JOIN, EXCEPT, or NOT EXISTS?

Answer 2

试试这个

SELECT * FROM taxonomy WHERE taxonomy_id NOT IN (SELECT parent_id FROM taxonomy WHERE parent_id <> 0)

Answer 3

select taxonomy_id
from taxonomy
where taxonomy_id not in
(
  select distinct parent_id from taxonomy
)

Answer 4

在MySQL中，你需要求助于相关的子查询。

要么不存在：

select t.*
from taxonomy t
where t.parent_id <> 0
and not exists (select 1 from taxonomy t2 where t2.parent_id <> t.taxonomy_id)

或不在：

select t.*
from taxonomy t
where t.parent_id <> 0
and t.taxonomy_id not in (select t2.parent_id from taxonomy t2)

Answer 5

可替换地：

select * from taxonomy where taxonomy_id <> all (select parent_id from taxonomy)

Demonstration

感谢用户Tim Schmelter优质服务sqlfiddle.com

的链接

如何只选择表中的子项

5 个答案: