text: -- alter acquisition table
  alter table acquisition.acquisitions
    alter column application_id type varchar using application_id::varchar,
    alter column operator_id type varchar using operator_id::varchar;
  
  -- alter errors table
  alter table acquisition.errors
    alter column operator_id type varchar using operator_id::varchar;
  
  -- update all 'unknown' values to 0
  update acquisition.acquisitions set application_id = 'unknown' where application_id = '0';
  