MYSQL 数据库给表加外键约束条件 (史上最详细教程)

下面是已经创建好的两个数据表!(还未加外键约束) 1. mysql> show columns from message;//信息表 +-----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------+--------------+------+-----+---------+----------------+ | m_id | int(11)