When the call sign is wpib, what is lowest ERP W?
CREATE TABLE "full_power_translators" (
  "call_sign" text,
  "frequency_m_hz" real,
  "city_of_license" text,
  "erp_w" real,
  "class" text,
  "fcc_info" text
);
SELECT MIN("erp_w") FROM "full_power_translators" WHERE "call_sign"='wpib';