Answers for "what to do if we have to add new column in existing migration"

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add a new column to existing table in a migration

// for Laravel 5+
php artisan make:migration add_email_to_users_table --table=users

public function up()
{
    Schema::table('users', function($table) {
        $table->integer('email');
    });
}

public function down()
{
    Schema::table('users', function($table) {
        $table->dropColumn('email');
    });
}

php artisan migrate

add new column in existing table in laravel migration

public function up()
{
    Schema::table('users', function($table) {
        $table->integer('paid');
    });
}