What is the callsign that has a station type of relay and a channel number of TV-2?
CREATE TABLE "ptv_stations_nationwide" (
  "branding" text,
  "callsign" text,
  "ch_num" text,
  "power_k_w" text,
  "station_type" text,
  "location_transmitter_site" text
);
SELECT "callsign" FROM "ptv_stations_nationwide" WHERE "station_type"='Relay' AND "ch_num"='TV-2';