MySQL 中的分层查询
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Hierarchical queries in MySQL
提问by Quassnoi
I'm trying to find all the parents, grandparents, etc. of a particular field with any depth. For example, given the below structure, if I provide 5, the values returned should be 1, 2, 3 and 4.
我试图找到具有任何深度的特定领域的所有父母、祖父母等。例如，给定下面的结构，如果我提供 5，返回的值应该是 1、2、3 和 4。
| a | b |
-----------
| 1 | 2 |
| 2 | 3 |
| 3 | 4 |
| 4 | 5 |
| 3 | 6 |
| 4 | 7 |
How would I do this?
我该怎么做？
回答by Quassnoi
SELECT @id :=
(
SELECT senderid
FROM mytable
WHERE receiverid = @id
) AS person
FROM (
SELECT @id := 5
) vars
STRAIGHT_JOIN
mytable
WHERE @id IS NOT NULL
回答by Praxis Ashelin
The following answer is not MYSQL-only, but uses PHP. This answer can be useful for all those that end up on this page during their search (as I did) but are not limited to using MYSQL only.
以下答案不是仅限 MYSQL，而是使用 PHP。这个答案对所有在搜索过程中最终出现在此页面上的人（就像我所做的那样）都很有用，但不仅限于仅使用 MYSQL。
If you have a database with a nested structure of unknown depth, you can print out the contents using a recursive loop:
如果您的数据库具有未知深度的嵌套结构，则可以使用递归循环打印出内容：
function goDownALevel($parent){
$children = $parent->getChildren(); //underlying SQL function
if($children != null){
foreach($children as $child){
//Print the child content here
goDownALevel($child);
}
}
}
This function can also be rewritten in any other language like Javascript.
此函数也可以用任何其他语言（如 Javascript）重写。
