翻译 InnoDB permits a foreign key to reference any index column or group of columns. However, in the referenced table, there must be an index where the referenced columns are the first columns in the same order. Hidden columns that InnoDB adds to an index are also considered (see Section 14.6.2.1, “Clustered and Secondary Indexes”).

答：InnoDB允许外键引用任何索引列或列组。但是，在被引用的表中，必须有一个索引，其中被引用的列必须以相同的顺序作为第一列。 InnoDB添加到索引的隐藏列也是如此（参见14.6.2.1节“聚簇索引和二级索引”）。