来自 外键约束

如果你重新创建一个表删除，它必须有一个定义符合外键的引用它的约束.它必须有正确的列名和类型，并且它必须有索引引用的键，如前所述.如果这些不满足，MySQL返回错误编号 1005 并指错误错误消息中的 150.

If you re-create a table that was dropped, it must have a definition that conforms to the foreign key constraints referencing it. It must have the right column names and types, and it must have indexes on the referenced keys, as stated earlier. If these are not satisfied, MySQL returns error number 1005 and refers to error 150 in the error message.

我怀疑是因为您没有将 foo 创建为 InnoDB，因为其他一切看起来都不错.

My suspicion is that it's because you didn't create foo as InnoDB, as everything else looks OK.

来自同一页面 -

两个表都必须是 InnoDB 表并且它们不能是 TEMPORARY 表.

Both tables must be InnoDB tables and they must not be TEMPORARY tables.