Let's have an up and down migration

db/migrations/20181213125806_add_parent_field.php

@@ -30,17 +30,29 @@ class AddParentField extends AbstractMigration
      * Remember to call "create()" or "update()" and NOT "save()" when working
      * with the Table class.
      */
-    public function change()
+    public function up()
     {
         $table = $this->table('contreparties');
-        $table->addColumn('parent', 'integer');
-        $table->update();
+        if (!$table->hasColumn('parent')) {
+            $table->addColumn('parent', 'integer');
+            $table->save();
+        }
 
         // Let's set some default value
         $builder = $this->getQueryBuilder();
-        $stmt = $builder->update('contreparties')
+        $stmt = $builder->update('contreparties', 'c')
             ->set('parent', 'id')
-            ->where(['parent' => ''])
+//            ->where('parent = 0')
             ->execute();
     }
+
+    public function down()
+    {
+        $table = $this->table('contreparties');
+
+        if ($table->hasColumn('parent')) {
+            $table->removeColumn('parent')
+                ->save();
+        }
+    }
 }