Add an index on the events.type column for faster SELECT DISTINCT() queries

migrations/20181021154055-index-on-type.js

@@ -0,0 +1,16 @@
+'use strict';
+
+const indexName ='events_type_index';
+
+module.exports = {
+  up: (queryInterface, Sequelize) => {
+    return queryInterface.addIndex('events', {
+      name:  indexName,
+      fields: ['type'],
+    });
+  },
+
+  down: (queryInterface, Sequelize) => {
+    return queryInterface.removeIndex('events', indexName);
+  }
+};