先來看數據表的結構如下：
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
我要的要求是根據一個分類ID（這個分類ID可能是一個子分類），得到所有的父分類，下面是相應的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
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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
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