Make pipeline / stage position index not unique

db/migrate/20180530135500_add_index_to_stages_position.rb

@@ -6,7 +6,7 @@ class AddIndexToStagesPosition < ActiveRecord::Migration
   disable_ddl_transaction!
   def up
-    add_concurrent_index :ci_stages, [:pipeline_id, :position], unique: true
+    add_concurrent_index :ci_stages, [:pipeline_id, :position]
   end
   def down

db/schema.rb

@@ -518,7 +518,7 @@ ActiveRecord::Schema.define(version: 20180530135500) do
   end
   add_index "ci_stages", ["pipeline_id", "name"], name: "index_ci_stages_on_pipeline_id_and_name", unique: true, using: :btree
-  add_index "ci_stages", ["pipeline_id", "position"], name: "index_ci_stages_on_pipeline_id_and_position", unique: true, using: :btree
+  add_index "ci_stages", ["pipeline_id", "position"], name: "index_ci_stages_on_pipeline_id_and_position", using: :btree
   add_index "ci_stages", ["pipeline_id"], name: "index_ci_stages_on_pipeline_id", using: :btree
   add_index "ci_stages", ["project_id"], name: "index_ci_stages_on_project_id", using: :btree