需求：
在樹形的節點關係下，比如選單樹或者檔案目錄樹，要想獲取某個節點的所有子節點，或者所有父類節點，在知道節點樹最大層級的情況下，可以直接通過一條sql直接查詢實現
表結構：
id, parent_id
eg: 已知節點樹深度不超過10， 查詢id=100010的節點的所有子節點
select
org.id as id,
concat(
'[',
concat_ws(',',
group_concat( distinct pa1.id ),
group_concat( distinct pa2.id ),
group_concat( distinct pa3.id ),
group_concat( distinct pa4.id ),
group_concat( distinct pa5.id ),
group_concat( distinct pa6.id ),
group_concat( distinct pa7.id ),
group_concat( distinct pa8.id ),
group_concat( distinct pa9.id ),
group_concat( distinct pa10.id ) ),
']'
) as child_ids
from organization org
left join organization pa1 on org.id=pa1.parent_id
left join organization pa2 on pa1.id=pa2.parent_id
left join organization pa3 on pa2.id=pa3.parent_id
left join organization pa4 on pa3.id=pa4.parent_id
left join organization pa5 on pa4.id=pa5.parent_id
left join organization pa6 on pa5.id=pa6.parent_id
left join organization pa7 on pa6.id=pa7.parent_id
left join organization pa8 on pa7.id=pa8.parent_id
left join organization pa9 on pa8.id=pa9.parent_id
left join organization pa10 on pa9.id=pa10.parent_id
where org.id=100010
group by org.id;
id, child_ids
100, [1,2,3,4]
已知節點樹深度不超過10， 查詢id=100038的節點的所有父節點
select
org.id,
concat(
'[',
concat_ws(',',
zo.parent_id,
pa1.parent_id,
pa2.parent_id,
pa3.parent_id,
pa4.parent_id,
pa5.parent_id,
pa6.parent_id,
pa7.parent_id,
pa8.parent_id,
pa9.parent_id,
pa10.parent_id ),
']'
) as parent_ids
from organization org
left join organization pa1 on pa1.id=org.parent_id
left join organization pa2 on pa2.id=pa1.parent_id
left join organization pa3 on pa3.id=pa2.parent_id
left join organization pa4 on pa4.id=pa3.parent_id
left join organization pa5 on pa5.id=pa4.parent_id
left join organization pa6 on pa6.id=pa5.parent_id
left join organization pa7 on pa7.id=pa6.parent_id
left join organization pa8 on pa8.id=pa7.parent_id
left join organization pa9 on pa9.id=pa8.parent_id
left join organization pa10 on pa10.id=pa9.parent_id
where org.id=100038
id, parent_ids
100, [1,2,3,4]
注group_concat(field_name separator 『,』) 分組合併某列， 即將分組後每組資料的某列合併為一行資料（多行資料合併為一行，只針對一列）
group_concat()中的值為你要合併的資料的欄位名;
separator 函式是用來分隔這些要合併的資料的；
』 '中是你要用哪個符號來分隔，預設使用 ','分隔；
注：group_concat只有與group by語句同時使用才能產生效果，需要將拼接的結果去重的話，可與distinct結合使用即可。
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