如何僅使用與SQL父表子關係選擇一代分層樹？

Question

比方說，有一個叫人有以下的列表：

• 爲person_id（整數）
• parent_person_id（整數）
• 名（爲varchar）

現在，讓我們說表正在填充，名稱值只是字母（A，B，C，D ...）。考慮到每個人的父母，我們最終會得到像下面那樣的分層樹。這些值是在格式：

爲person_id，parent_person_id，名稱

• 1，1，A
• 2,2，B
  • 3，2，C
    • 4，3，D
  • 5，2，E
    • 6,5，F
      • 7,6，G
      • 8,6，H

考慮在以上的結構中，A & B作爲第一代，C & E作爲第二代，D第三代210 F，第四代G & H.對於第一代元素，parent_person_id等於元素的person_id。

我需要編寫一個查詢，允許我從樹的特定代（第一，第二，第三，第四等）中選擇名稱。因此，我可以得到一個表格，其中包含特定用戶的姓名。例如：

第一代

person name | parent name 
A   | A 
B   | B 

第二代

person name | parent name 
C   | B 
E   | B 

第三代

person name | parent name 
D   | C 
F   | E 

第四代

person name | parent name 
G   | F 
H   | F 

我想通過一個參數來定義每一代應該在下面的查詢中被列爲子。

SELECT 
    child.name as 'person name', 
    parent.name as 'parent name' 
FROM 
    people as child 
JOIN 
    people as parent 
ON 
    child.parent_person_id = parent.person_id 
WHERE 
    -- I NEED HELP HERE :) 
; 

有沒有人有任何想法，我怎麼能做到這一點？歡迎任何幫助。

Answer 1

這是冗長而醜陋的，並且會很慢，它只限於4代，但我不知道該怎麼辦。

SELECT person_name, parent_name FROM 

    (SELECT child1.name AS person_name, parent1.name AS parent_name, '1' AS generation 
    FROM people as child1 
    JOIN people as parent1 
    ON child1.parent_person_id = parent1.person_id AND child1.parent_person_id = child1.person_id 

    UNION 

    SELECT child2.name AS person_name, parent2.name AS parent_name, '2' AS generation 
    FROM people as child2 
    JOIN people as parent2 
    ON child2.parent_person_id = parent2.person_id AND child2.parent_person_id <> child2.person_id AND parent2.parent_person_id = parent2.person_id 

    UNION 

    SELECT child3.name AS person_name, parent3.name AS parent_name, '3' AS generation 
    FROM people as child3 
    JOIN people as parent3 
    ON child3.parent_person_id = parent3.person_id AND parent3.parent_person_id <> parent3.person_id 
    JOIN people as grandparent1 
    ON parent3.parent_person_id = grandparent1.person_id AND grandparent1.parent_person_id = grandparent1.person_id 

    UNION 

    SELECT child4.name AS person_name, parent4.name AS parent_name, '4' AS generation 
    FROM people as child4 
    JOIN people as parent4 
    ON child4.parent_person_id = parent4.person_id AND parent4.parent_person_id <> parent4.person_id 
    JOIN people as grandparent2 
    ON parent4.parent_person_id = grandparent2.person_id AND grandparent2.parent_person_id <> grandparent2.person_id 
    JOIN people as greatgrandparent 
    ON grandparent2.parent_person_id = greatgrandparent.person_id AND greatgrandparent.parent_person_id = greatgrandparent.person_id 
    ) AS tree 

WHERE generation = ?