time difference in words for postgres

time_diff_in_words.sql

create or replace function time_diff_in_words(
    a timestamp with time zone,
    b timestamp with time zone
) returns text as $$
declare
    _age interval;
    _suffix text;
    _years integer;
    _months integer;
    _days integer;
    _hours integer;
    _minutes integer;
    _seconds integer;
    _year_part text;
    _month_part text;
    _day_part text;
    _hour_part text;
    _minute_part text;
    _second_part text;
    _parts text ARRAY;
begin
    _age          = age(a,b);
    _suffix       = case when a > b then ' ago' else ' from now' end;
    _years        = abs(date_part('year',   _age));
    _months       = abs(date_part('month',  _age));
    _days         = abs(date_part('day',    _age));
    _hours        = abs(date_part('hour',   _age));
    _minutes      = abs(date_part('minute', _age));
    _seconds      = abs(date_part('second', _age));
    _year_part    = case when _years   = 1 then '1 year'   else _years   || ' years'   end;
    _month_part   = case when _months  = 1 then '1 month'  else _months  || ' months'  end;
    _day_part     = case when _days    = 1 then '1 day'    else _days    || ' days'    end;
    _hour_part    = case when _hours   = 1 then '1 hour'   else _hours   || ' hours'   end;
    _minute_part  = case when _minutes = 1 then '1 minute' else _minutes || ' minutes' end;
    _second_part  = case when _seconds = 1 then '1 second' else _seconds || ' seconds' end;
    if _years   > 0 then _parts = array_append(_parts, _year_part);   end if;
    if _months  > 0 then _parts = array_append(_parts, _month_part);  end if;
    if _days    > 0 then _parts = array_append(_parts, _day_part);    end if;
    if _hours   > 0 then _parts = array_append(_parts, _hour_part);  end if;
    if _minutes > 0 then _parts = array_append(_parts, _minute_part); end if;
    if _seconds > 0 then _parts = array_append(_parts, _second_part); end if;
    return array_to_string(_parts, ', ') || _suffix;
end;
$$ language plpgsql volatile;