帮助编写嵌套集的SQL查询

Question

我正在使用嵌套集将数据库存储在数据库中.表的字段是id,lft,rgt和name.

给定一个节点ID,我需要找到它们本身就是叶节点的所有直接子节点(不是孙子节点).

Answer 1

文章在MySQL管理层次数据给出了如何使用嵌套集合一个很好的例子,并给出了许多常见的查询,包括这一个例子.

这是如何找到节点的直接子节点:

SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth
FROM nested_category AS node,
    nested_category AS parent,
    nested_category AS sub_parent,
    (
        SELECT node.name, (COUNT(parent.name) - 1) AS depth
        FROM nested_category AS node,
        nested_category AS parent
        WHERE node.lft BETWEEN parent.lft AND parent.rgt
        AND node.name = '**[[MY NODE]]**'
        GROUP BY node.name
        ORDER BY node.lft
    )AS sub_tree
WHERE node.lft BETWEEN parent.lft AND parent.rgt
    AND node.lft BETWEEN sub_parent.lft AND sub_parent.rgt
    AND sub_parent.name = sub_tree.name
GROUP BY node.name
HAVING depth = 1
ORDER BY node.lft;

然后将它与叶子节点rgt等于的事实相结合,然后进行lft + 1设置._{原谅双关语.}