Hello!

Sometimes working with Foreign Key could be complex to starters. The most common case that I see is when you try to FK a column with a different type.

CREATE TABLE IF NOT EXISTS `countries` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
);

CREATE TABLE IF NOT EXISTS `country_states` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`country_id` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`)
);

It is a good example. `id_country` is a INT, but `countries.id` is BIGINT. And when try to create a FK for it we will got:

SQL Error (1005): Can't create table `country_states` (errno: 150 "Foreign key constraint is incorrectly formed")

The error is correct, but is not clear about "what is wrong". My suggestion is update the description to some more... descriptive:

SQL Error (1005): Can't create table `country_states` (errno: 150 "Foreign key constraint is incorrectly formed: country_states.country_id must be a BIGINT")

However, I don't know if it is the role of the server to report something in more detail like this.