mysql删除父节点

-- 创建父表
CREATE TABLE parent_table (
    id INT PRIMARY KEY,
    name VARCHAR(255)
);

-- 创建子表
CREATE TABLE child_table (
    id INT PRIMARY KEY,
    name VARCHAR(255),
    parent_id INT,
    FOREIGN KEY (parent_id) REFERENCES parent_table(id)
);

-- 添加级联删除约束
ALTER TABLE child_table
ADD CONSTRAINT fk_child_parent
FOREIGN KEY (parent_id)
REFERENCES parent_table(id)
ON DELETE CASCADE;

-- 删除父节点
DELETE FROM parent_table WHERE id = 1;

-- 先删除子节点
DELETE FROM child_table WHERE parent_id = 1;
-- 再删除父节点
DELETE FROM parent_table WHERE id = 1;

-- 添加设置为空约束
ALTER TABLE child_table
ADD CONSTRAINT fk_child_parent
FOREIGN KEY (parent_id)
REFERENCES parent_table(id)
ON DELETE SET NULL;

-- 删除父节点
DELETE FROM parent_table WHERE id = 1;