MySQL - 仅获取特定父级的子级

Question

如果我运行以下查询：

SELECT loc2.* FROM `locations` AS loc
INNER JOIN `locations` AS loc2 ON loc.location_id = loc2.location_parent
WHERE loc.location_status='publish'

我得到以下结果：

+-------------+------------------+-----------------+-----------------+
| location_id | location_name    | location_parent | location_status |
+-------------+------------------+-----------------+-----------------+
|          19 | Dhaka Division   |             564 | publish         |
|          22 | Dhaka District   |              19 | publish         |
|          26 | Dhaka City       |              22 | publish         |
|          28 | Mirpur           |              26 | publish         |
|          30 | Mirpur - 12      |              28 | publish         |
|          32 | Mirpur DOHS      |              30 | publish         |
|         634 | Gazipur District |              19 | publish         |
+-------------+------------------+-----------------+-----------------+
7 rows in set (0.00 sec)

实际上我正在尝试从数据库中获取所有孩子/孙子女。现在，上面的查询只是根据父子规则对行进行排序并返回所有行。但是，我想为SQL添加一个条件，以便它只获取特定父级的子级。

例如，我想获取19的所有子行/节点/位置。结果集应如下：

+-------------+------------------+-----------------+-----------------+
| location_id | location_name    | location_parent | location_status |
+-------------+------------------+-----------------+-----------------+
|          22 | Dhaka District   |              19 | publish         |
|          26 | Dhaka City       |              22 | publish         |
|          28 | Mirpur           |              26 | publish         |
|          30 | Mirpur - 12      |              28 | publish         |
|          32 | Mirpur DOHS      |              30 | publish         |
+-------------+------------------+-----------------+-----------------+

我试过这个：

SELECT loc2.* FROM `locations` AS loc
INNER JOIN `locations` AS loc2 ON loc.location_id = loc2.location_parent
WHERE loc.location_status='publish' AND loc2.location_parent=19

和此：

SELECT loc2.* FROM `locations` AS loc
INNER JOIN `locations` AS loc2 ON loc.location_id = loc2.location_parent
WHERE loc.location_status='publish' AND loc.location_parent=19

但他们都应该返回相同的结果：

+-------------+------------------+-----------------+-----------------+
| location_id | location_name    | location_parent | location_status |
+-------------+------------------+-----------------+-----------------+
|          22 | Dhaka District   |              19 | publish         |
+-------------+------------------+-----------------+-----------------+

那么，我该怎么做才能达到我需要的效果呢？

Answer 1

实际上，这是一个称为递归的数据库的高级主题，您的要求是从最顶层的父级及其所有子级，孙子级等获取数据树。

其他DBMS提供了解决此类问题的功能，例如Microsoft SQL Server调用其解决方案CTE（Common Table Express），但是这在mySQL中很长，并且没有简单的解决方案来解决您的问题。但是，您可以在mysql中搜索递归以获取有关此主题的更多详细信息。

Answer 2

您正在寻找的是＆＃34;关闭＆＃34;表。这本质上是一个表，用于保持分层数据的子，父和深度的引用。

我在这里发现了一篇很棒的帖子，可以帮助你达到理想的效果。 What are the options for storing hierarchical data in a relational database?