When you create a migration using a command such as:
php artisan make:migration category
A migration file is created. As yet, the migration hasn't been made i.e. the resulting table hasn't been created. This gives you the chance to develop the migration file.
2 functions exist by default in the migration file; up() and down().
up() is commonly used to create a table.
down() is commonly used to delete the table.
When a migration has been made, it is added to the migrations table. As well as the migration name is a batch number. The batch number works in co-ordination with the down() function and the rollback command.
If you would like to go back a step, perhaps you have made a mistake, you can use the command:
php artisan migrate:rollback
This command, looks at the migrations table. It looks at the latest batch numbers and reverts the migrations with the latest batch number. It reverts those migrations by performing whatever is contained in the down() functions of those migration files.
You can see how it would be possible to selectively reverse migrations. All you have to do, is apply the latest batch number to the ones you want to reverse.
