先来看数据表的结构如下：
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
我要的要求是根据一个分类ID（这个分类ID可能是一个子分类），得到所有的父分类，下面是相应的SQL：
方式一：
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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 <> 2
union all select @r, parent_id,@l+1 FROM table1 WHERE id = @r
) T1
JOIN table1 T2
ON T1._id = T2.id
ORDER BY T1.lvl DESC |
方式二：
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SELECT T2.id, T2.name FROM (
SELECT @r AS _id,
@stop:=@stop+if(@r=2,1,@stop) as stop,
(SELECT @r := parent_id FROM table1 WHERE id = _id) AS parent_id,
@l := @l + 1 AS lvl
FROM (SELECT @r := 5, @l := 0, @stop:=0) vars,
table1 h
WHERE @stop < 1) T1
JOIN table1 T2
ON T1._id = T2.id
ORDER BY T1.lvl DESC |