postgresql postgres 中的 ON DELETE SET NULL
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ON DELETE SET NULL in postgres
提问by tamikoon
HI I'm new to postgresql environment so been lost for a while. I want to keep my data when parent entity is deleted. I want to know how to make 'ON DELETE SET NULL' for postgresql database. Please give me a clue.
嗨，我是 postgresql 环境的新手，所以迷路了一段时间。我想在删除父实体时保留我的数据。我想知道如何为 postgresql 数据库制作“ON DELETE SET NULL”。请给我一个线索。
回答by Craig Ringer
ON DELETE SET NULLis a standard foreign key constraint option.
ON DELETE SET NULL是标准的外键约束选项。
CREATE TABLE some_child (
parent_id integer references parent(id) on delete set null
);
or:
或者：
ALTER TABLE some_child
ADD CONSTRAINT parent_id_fk
FOREIGN KEY (parent_id) REFERENCES parent(id)
ON DELETE SET NULL;
See the documentation.
请参阅文档。
In future posts make sure you include your PostgreSQL version and explain what you've already tried.
在以后的帖子中，请确保包含您的 PostgreSQL 版本并解释您已经尝试过的内容。
