MySQL’s InnoDB storage engine supports the use of foreign key constraints, which are very useful but require you to manage your data in a much more rigorous manner than might otherwise be employed when not taking advantage of this feature. For instance, when migrating data from a database which does not use foreign keys to one which does, you’ll often encounter an error in which MySQL complains about a foreign key constraint not being met. This is easily resolved by temporarily disabling foreign key checks before beginning the import, and then re-enabling them when the import is complete.
To disable foreign key checks, add the following line to the top of your import file:
SET foreign_key_checks = 0
You’ll of course want to re-enable foreign key constraint checks following the import, so add the following line to the end of your import file:
SET foreign_key_checks = 1