问题描述
我有一个简单的 MySQL 表，其中包含一个类别列表，级别由 parent_id 决定:
I have a simple MySQL table thats contains a list of categories, level is determined by parent_id:
id name parent_id
---------------------------
1 Home 0
2 About 1
3 Contact 1
4 Legal 2
5 Privacy 4
6 Products 1
7 Support 1
我正在尝试制作面包屑路径.所以我有孩子的id"，我想得到所有可用的父母(迭代链直到我们到达 0家").可以有任意数量或子行进入无限深度.
I'm attempting to make a breadcrumb trail. So i have the 'id' of the child, I want to get all available parents (iterating up the chain until we reach 0 "Home"). There could be any number or child rows going to an unlimited depth.
目前我正在为每个父级使用 SQL 调用，这很麻烦.SQL 中有没有办法在一个查询中完成所有这些操作?
Currently I am using an SQL call for each parent, this is messy. Is there a way in SQL to do this all on one query?
推荐答案
改编自 这里:
SELECT T2.id, T2.name
FROM (
SELECT
@r AS _id,
(SELECT @r := parent_id FROM table1 WHERE id = _id) AS parent_id,
@l := @l + 1 AS lvl
FROM
(SELECT @r := 5, @l := 0) vars,
table1 h
WHERE @r <> 0) T1
JOIN table1 T2
ON T1._id = T2.id
ORDER BY T1.lvl DESC
行 @r := 5 是当前页面的页码.结果如下:
The line @r := 5 is the page number for the current page. The result is as follows:
1, 'Home'
2, 'About'
4, 'Legal'
5, 'Privacy'
这篇关于在一个 SQL 查询中获取所有父行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编程学习网！