text: -- Your SQL goes here
  ALTER TABLE bike_data 
  ALTER COLUMN created_at DROP DEFAULT,
  ALTER COLUMN created_at TYPE bigint 
  USING extract(epoch from created_at);
  
  ALTER TABLE oven_data
  ALTER COLUMN created_at DROP DEFAULT,
  ALTER COLUMN created_at TYPE bigint 
  USING extract(epoch from created_at);
  
  ALTER TABLE solar_microgrid_data
  ALTER COLUMN created_at DROP DEFAULT,
  ALTER COLUMN created_at TYPE bigint 
  USING extract(epoch from created_at);
  