MySQL父子一个查询选择

Question

我有一个MySQL表,字段如下:

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,Fruit id为1,而Orange是其中之一,因此父级为1.

但是,我想做一个有效的MySQL查询来获取格式为parent-> children-> parent-> children格式的所有记录.我怎样才能做到这一点？

查询的结果记录应如下所示:

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

Answer 1

你需要一个mysql不支持的递归连接.你唯一能做的就是确定最大深度(你的情况是1,因为你有p-> c),你可以确定所需的连接数:

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个自连接:

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