检查以下表是否在其记录之间具有某种关系将是有用的:
-- Table: privilege_group
CREATE TABLE privilege_group (
privilege_group_id integer NOT NULL CONSTRAINT privilege_group_pk PRIMARY KEY AUTOINCREMENT,
name text NOT NULL,
CONSTRAINT privilege_group_name UNIQUE (name)
);
-- Table: privilege_relationship
CREATE TABLE privilege_relationship (
privilege_relationship_id integer NOT NULL CONSTRAINT privilege_relationship_pk PRIMARY KEY AUTOINCREMENT,
parent_id integer NOT NULL,
child_id integer NOT NULL,
CONSTRAINT privilege_relationship_parent_child UNIQUE (parent_id, child_id),
CONSTRAINT privilege_relationship_parent_id FOREIGN KEY (parent_id)
REFERENCES privilege_group (privilege_group_id),
CONSTRAINT privilege_relationship_child_id FOREIGN KEY (child_id)
REFERENCES privilege_group (privilege_group_id),
CONSTRAINT privilege_relationship_check CHECK (parent_id != child_id)
);
父母可以有很多孩子,孩子可以有很多父母。编写代码来处理数据库之外的记录总是可行的,但是是否可以使用深度优先(或广度优先)搜索来检查孩子是否有特定父母?
My related question收到了来自CL.的评论,提到了WITH clause,但我对分层查询的经验相当有限,不足以理解,选择和应用页面上的示例到我的目标:
有人可以告诉我如何知道一个孩子是否有父母,如果知道两者的名字?
这是标准树搜索(使用UNION而不是UNION ALL来防止无限循环):
WITH RECURSIVE ParentsOfG1(id) AS (
SELECT privilege_group_id
FROM privilege_group
WHERE name = 'G1'
UNION
SELECT parent_id
FROM privilege_relationship
JOIN ParentsOfG1 ON id = child_id
)
SELECT id
FROM ParentsOfG1
WHERE id = (SELECT privilege_group_id
FROM privilege_group
WHERE name = 'P2');
深度/广度优先对此无关紧要。
CL.'s answer的替代方法可能是此查询已被重新格式化并调整为使用绑定参数,这些参数可插入需要检查某些关系的项目中:
WITH RECURSIVE parent_of_child(id)
AS (
SELECT privilege_group_id
FROM privilege_group
WHERE name = :child
UNION
SELECT parent_id
FROM privilege_relationship
JOIN parent_of_child
ON id = child_id)
SELECT id
FROM parent_of_child
WHERE id = (
SELECT privilege_group_id
FROM privilege_group
WHERE name = :parent)