使用具有自引用外键的表:
CREATE TABLE tree (
id INTEGER,
parent_id INTEGER,
PRIMARY KEY (id)
);
ALTER TABLE tree
ADD CONSTRAINT fk_tree
FOREIGN KEY (parent_id)
REFERENCES tree(id);
INSERT INTO tree (id, parent_id)
VALUES (1, null),
(2, 1),
(3, 1),
(4, 2),
(5, null),
(6, 5);
我希望通过递归遍历树删除分支,因为我可能不使用ON DELETE CASCADE
。
WITH RECURSIVE branch (id, parent_id) AS (
SELECT id, parent_id
FROM tree
WHERE id = 1 -- Delete branch with root id = 1
UNION ALL SELECT c.id, c.parent_id
FROM tree c -- child
JOIN branch p -- parent
ON c.parent_id = p.id
)
DELETE FROM tree t
USING branch b
WHERE t.id = b.id;
使用Postgres中的公用表表达式是否安全,或者我是否必须担心删除记录的顺序? Postgres会将所有行删除为单个集合,还是逐个删除?
如果答案取决于版本,从哪个版本删除安全?
不,您不必担心选择中的顺序。
外键(与唯一约束不同)是按语句计算的,而不是按行计算。并且公共表表达式仍然是单个语句,即使您有多个SELECT和DELETE。
因此,如果语句结束时所有约束仍然有效,则一切正常。
您可以通过以下简单测试轻松查看:
CREATE TABLE fk_test
(
id integer PRIMARY KEY,
parent_id integer,
FOREIGN KEY (parent_id) REFERENCES fk_test (id)
);
INSERT INTO fk_test (id, parent_id)
VALUES
(1, null),
(2, 1),
(3, 2),
(4, 1);
因此,即使以“错误”顺序指定ID,以下内容显然也有效:
DELETE FROM fk_test
WHERE id IN (1,2,3,4);
以下也有效 - 显示CTE仍然是单个语句:
with c1 as (
delete from fk_test where id = 1
), c2 as (
delete from fk_test where id = 2
), c3 as (
delete from fk_test where id = 3
)
delete from fk_test where id = 4;