深度嵌套的子查询，用于遍历MySQL中的树 [英] Deeply nested subqueries for traversing trees in MySQL

问题描述

我的数据库中有一个表，其中使用混合嵌套集(MPTT)模型(具有lft和rght值的模型)和邻接列表模型(将parent_id存储在每个节点).

I have a table in my database where I store a tree structure using the hybrid Nested Set (MPTT) model (the one which has lft and rght values) and the Adjacency List model (storing parent_id on each node).

my_table (id, parent_id, lft, rght, alias)

这个问题与树的MPTT方面无关，但是我认为如果有人对如何利用它有个好主意，我会保留.

我想将别名路径转换为特定节点.例如:"users.admins.nickf"将找到别名为"nickf"的节点，该节点是根的别名为"users"的子节点，别名为"admins". (parent_id, alias)上有一个唯一索引.

I want to convert a path of aliases to a specific node. For example: "users.admins.nickf" would find the node with alias "nickf" which is a child of one with alias "admins" which is a child of "users" which is at the root. There is a unique index on (parent_id, alias).

我首先编写该函数，以便它将路径拆分为各个部分，然后一个一个地查询数据库:

I started out by writing the function so it would split the path to its parts, then query the database one by one:

SELECT `id` FROM `my_table` WHERE `parent_id` IS NULL AND `alias` = 'users';-- 1
SELECT `id` FROM `my_table` WHERE `parent_id` = 1 AND `alias` = 'admins';   -- 8
SELECT `id` FROM `my_table` WHERE `parent_id` = 8 AND `alias` = 'nickf';    -- 37

但是后来我意识到，使用可变数量的嵌套，我可以通过一个查询来做到这一点:

But then I realised I could do it with a single query, using a variable amount of nesting:

SELECT `id` FROM `my_table` WHERE `parent_id` = (
    SELECT `id` FROM `my_table` WHERE `parent_id` = (
        SELECT `id` FROM `my_table`
        WHERE `parent_id` IS NULL AND `alias` = 'users'
    ) AND `alias`  = 'admins'
) AND `alias` = 'nickf';

由于子查询的数量取决于路径中的步骤数，因此我会遇到太多子查询的问题吗? (如果甚至有这样的事情)

Since the number of sub-queries is dependent on the number of steps in the path, am I going to run into issues with having too many subqueries? (If there even is such a thing)

是否有更好/更智能的方法来执行此查询?

Are there any better/smarter ways to perform this query?

推荐答案

这项工作有效吗?

select r0.id 
  from my_table as r0 
  join my_table as r1 on(r0.parent_id = r1.id) 
  join my_table as r2 on(r1.parent_id = r2.id)
 where r0.alias='nickf'
   and r1.alias='admins'
   and r2.alias='users'
   and r2.parent_id is null

在我看来，实际上并不需要嵌套的子查询..

Seems to me there is not really a need for nested subqueries ..

还是我错了，缺少什么?

or am I wrong, missing something?

这篇关于深度嵌套的子查询，用于遍历MySQL中的树的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！