What are Unit 2's dates of commissioning?
CREATE TABLE "installed_capacity" (
  "stage" text,
  "unit_number" real,
  "installed_capacity_mw" text,
  "date_of_commissioning" text,
  "status" text,
  "tg_set_provider" text,
  "boiler_provider" text
);
SELECT COUNT("date_of_commissioning") FROM "installed_capacity" WHERE "unit_number"=2;