Name the build date for total produced of 146
CREATE TABLE "switchers_s_series" (
  "model" text,
  "specification" text,
  "build_date" text,
  "total_produced" real,
  "wheel_arrangement" text,
  "prime_mover" text,
  "power_output" text
);
SELECT "build_date" FROM "switchers_s_series" WHERE "total_produced"=146;