What is the frequency of the Chennai Egmore Dibrugarh Express to Dibrugarh?
CREATE TABLE "train_services" (
  "train_no" text,
  "train_name" text,
  "origin" text,
  "destination" text,
  "frequency" text
);
SELECT "frequency" FROM "train_services" WHERE "destination"='dibrugarh' AND "train_name"='chennai egmore dibrugarh express';