Re: GENERATE AS

4. ALTER TABLE auto_auth.matt

               ADD column matt_hour INT  GENERATED ALWAYS AS (date_part('hour', current_timestamp)::INT - date_part('hour', matt_time)::INT) stored       

              

               ERROR:  generation expression is not immutable

SQL state: 42P17

You can use only immutable functions to generate columns. Timestamp with time zone as an argument makes function not immutable because timezone could be set locally and  results could differ depending on timezone