Question

我正在尝试从类别表中获取顶级父ID：

+-------------+----------------------+--------+
| category_id | name                 | parent |
+-------------+----------------------+--------+
|           1 | ELECTRONICS          |   NULL |
|           2 | TELEVISIONS          |      1 |
|           3 | TUBE                 |      2 |
|           4 | LCD                  |      2 |
|           5 | PLASMA               |      2 |
|           6 | PORTABLE ELECTRONICS |      1 |
|           7 | MP3 PLAYERS          |      6 |
|           8 | FLASH                |      7 |
|           9 | CD PLAYERS           |      6 |
|          10 | 2 WAY RADIOS         |      6 |
+-------------+----------------------+--------+

可能有很多子类别，我的问题是如何获得子类别的最高父级？例如，在数据库子类别中，节点可以如下所示：
父＆GT;＆GT;子类别＆GT;＆GT; subsubcategory＆GT;＆GT; subsubsubcategory
另一个节点可能如下所示：
父＆GT;＆GT;子类别

因此，如果我查询id = 6的子类别的顶级父级，我会得到电子等等如何用mysql获取顶级父ID？我希望，这完全可以理解。

Answer 1

您必须编写一个循环查询的存储函数：

查询以查找父级

SELECT parent FROM cat WHERE category_id = 6

存储功能以查找顶级父级

DELIMITER $$

CREATE FUNCTION top_parent(PCat INTEGER) RETURNS INTEGER
BEGIN
  DECLARE MyParent INTEGER;
  DECLARE PrevParent INTEGER;
  SET PrevParent = PCat;
  REPEAT
    SELECT parent INTO MyParent FROM cat WHERE category_id = PrevParent;
    IF NOT(MyParent IS NULL) THEN
      SET PrevParent = MyParent;
    END IF;
  UNTIL (MyParent IS NULL) 
  END REPEAT;
  RETURN PrevParent;
END $$

DELIMITER ;

如何在查询中使用该功能

SELECT name FROM cat WHERE category_id = top_parent(6)

Answer 2

@r := 7无论你在这里给出的category_id将获得它的所有父级和提供限制1将获得顶级父级

<小时/>

SELECT T2.*
FROM (
       SELECT
         @r AS _category_id,
         (SELECT @r := parent FROM categories WHERE category_id = _category_id) AS parent,
         @l := @l + 1 AS lvl
       FROM
         (SELECT @r := 7, @l := 0) vars,
         categories WHERE @r <> 0) T1
  JOIN categories T2
    ON T1._category_id = T2.category_id
ORDER BY T1.lvl DESC
LIMIT 1;

如何从嵌套类别表中获取顶级父级？

2 个答案: