MySQL父级子级一个查询选择 [英] MySQL parent children one query selection

问题描述

我有一个MySQL表，其字段如下:

I have a MySQL table with fields as below:

id            name             parent
1             Fruit             0
2             Meat              0
3             Orange            1
4             Beef              2

其中父字段表示上层ID.例如，水果id是1，橙色是水果之一，因此父对象是1.

where parent field means the upper level id. For example Fruit id is 1, and Orange is one of the fruit so the parent is 1.

但是我想做一个有效的MySQL查询来获取所有记录，格式为parent-> children-> parent-> children格式.我该怎么办?

However I want to do an efficient MySQL query to fetch all records in the format parent->children->parent->children format. How can I do that?

查询的结果记录应如下所示:

The result record of the query should look like:

id            name             parent
1             Fruit             0
3             Orange            1
2             Meat              0
4             Beef              2

推荐答案

您需要mysql不支持的递归联接.唯一可以做的就是确定最大深度(由于p-> c，所以我将其设置为1)，并以此确定所需的联接数:

You need a recursive join which mysql doesn't support. The only thing you can do is determine the maximum level of depth (i your case it 1 since you have p->c) and with this you can determine the number of joins needed :

最大深度=自连接数:

SELECT
    p.id as parent_id,
    p.name as parent_id,
    c1.id as child_id,
    c1.name as child_name
FROM 
    my_table p
LEFT JOIN my_table c1
    ON c1.parent = p.id
WHERE
    p.parent=0

例如，如果最大深度为3，则需要3个自联接:

For example if you max level of depth was 3 the you would need 3 self-joins:

SELECT
    p.id as parent_id,
    p.name as parent_id,
    c1.id as child_id_1,
    c1.name as child_name_1,
    c2.id as child_id_2,
    c2.name as child_name_2,
    c3.id as child_id_3,
    c3.name as child_name_3
FROM 
    my_table p
LEFT JOIN my_table c1
    ON c1.parent = p.id
LEFT JOIN my_table c2
    ON c2.parent = c1.id
LEFT JOIN my_table c3
    ON c3.parent = c2.id
WHERE
    p.parent=0

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