mysql中foreign key

-- 确保引用的列是主键或唯一键
ALTER TABLE child_table ADD CONSTRAINT fk_name FOREIGN KEY (child_column) REFERENCES parent_table(parent_column);

-- 检查数据类型是否匹配
ALTER TABLE child_table MODIFY child_column datatype;

-- 确保被引用的表存在
CREATE TABLE IF NOT EXISTS parent_table (
    parent_column datatype PRIMARY KEY
);

-- 确保外键约束名称唯一
ALTER TABLE child_table ADD CONSTRAINT unique_fk_name FOREIGN KEY (child_column) REFERENCES parent_table(parent_column);

ALTER TABLE child_table DROP FOREIGN KEY fk_name;

SHOW CREATE TABLE child_table;

SELECT * FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE TABLE_NAME = 'child_table' AND REFERENCED_TABLE_NAME IS NOT NULL;