我想通过一组可延迟的约束从两个相互依赖的表中删除行。为了简化这篇文章,我模拟了一个简单的数据库模式。
我希望从 SQL 事务/数据库补丁中的某个表“delete_from_me”中删除条目。问题是,我想在松开链接本身之前根据第二个表“constraining_table”中的选择进行删除。
下面是对这两个表的描述:
tab-quarantine=> \d delete_from_me
Table "public.delete_from_me"
Column | Type | Modifiers
-----------+-------------------+-----------
id | character varying | not null
extension | character varying | not null
Indexes:
"delete_from_me_pkey" PRIMARY KEY, btree (id)
tab-quarantine=> \d constraining_table
Table "public.constraining_table"
Column | Type | Modifiers
--------+-------------------+-----------
image | character varying | not null
type | character varying | not null
Foreign-key constraints:
"constraining_table_image_fkey" FOREIGN KEY (image) REFERENCES delete_from_me(id)
ON UPDATE CASCADE
ON DELETE RESTRICT DEFERRABLE
这是我刚刚在其中吹嘘的一些示例数据:
tab-quarantine=> SELECT * FROM delete_from_me;
id | extension
------------+-----------
12345abcde | png
(1 row)
tab-quarantine=> SELECT * FROM constraining_table;
image | type
------------+----------
12345abcde | select_me
(1 row)
这是我的交易:
BEGIN;
\set ON_ERROR_STOP 1
SET CONSTRAINTS ALL DEFERRED;
DELETE FROM delete_from_me WHERE id IN (
SELECT image FROM constraining_table WHERE type = 'select_me'
);
DELETE FROM constraining_table WHERE type = 'select_me';
COMMIT;
此交易失败。当我逐步完成并手动执行此操作时,我会看到以下错误消息:
ERROR: update or delete on table "delete_from_me" violates foreign key constraint "constraining_table_image_fkey" on table "constraining_table"
DETAIL: Key (id)=(12345abcde) is still referenced from table "constraining_table".
这似乎是一个很好的临时表候选者,但是我想知道为什么我不能按这个顺序删除,因为约束在事务结束之前不应该有效?