假设有一个名为 people 的表,其中包含以下列:
- person_id(整数)
- parent_person_id(整数)
- 名称(可变字符)
现在,假设表格已经被填充并且名称值只是字母(A、B、C、D ...)。考虑到每个人的 parent ,我们最终得到一个像下面这样的分层树。这些值的格式为:
person_id, parent_person_id, 姓名
- 1, 1, A
- 2, 2, B
- 3, 2, C
- 4、3、D
- 5, 2, 乙
- 6, 5, 女
- 7, 6, G
- 8, 6, H
- 6, 5, 女
- 3, 2, C
考虑上面的结构,A&B是第一代,C&E是第二代,D&F是第三代,G&H是第四代。对于第一代元素,parent_person_id 等于元素的 person_id。
我需要编写一个查询,允许我从树的某一代(第一代、第二代、第三代、第四代等)中选择名称。结果,我可以获得一个包含某一代用户名称的表。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
我想传递一个参数来定义每一代都应该在以下查询中列为子代。
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 :)
;
有人对我如何实现这一目标有任何想法吗?欢迎任何帮助。
最佳答案
这是冗长和丑陋的,而且会很慢,而且仅限于 4 代,但我不知道还能怎么做。
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 = ?
关于mysql - 如何使用 SQL 的表父子关系仅选择一代层次树?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/33859288/