Re: Variable constants ?

On 16/08/2019 09:27, Rich Shepard wrote:
> On Thu, 15 Aug 2019, stan wrote:
>
>> I need to put a few bossiness constants, such as a labor rate multiplier
>> in an application. I am adverse to hard coding these things. The best
>> plan
>> i have come up with so far is to store them in a table, which would have
>> only 1 row, and a column for each needed constant.
>>
>> Anyone have a better way to do this?
>>
>> Failing a better way is there some way I can limit this table to only
>> allow one row to exist?
>
> Stan,
>
> I've resolved similar issues with changing regulatory agency staff.
> For your
> application(s) I suggest a table like this:
>
> create table labor_rate_mult (
>   rate         real primary_key,
>   start_date      date not null,
>   end_date    date
> )
>
> This provides both a history of labor rate multipliers and the ability to
> select either the most current one or a previous one.
>
> If other factors affect the rate, add attribute columns for them.
>
> Regards,
>
> Rich
>
>
I think a better approach is to:

 * include time
 * store independent of timezone (avoids problems with daylight saving)
 * only have one timestamp

   DROP TABLE IF EXISTS labour_rate_mult;

   CREATE TABLE labour_rate_mult
   (
        rate_name         text,
        effective_start   timestamptz,
        rate_value        real,
        valid             boolean,
        PRIMARY KEY (rate_name, effective_start)
   );

   INSERT INTO labour_rate_mult
   (
        rate_name,
        effective_start,
        rate_value,
        valid
   )
   VALUES  -- test data omits time for clarity
        ('junior', '2001-02-01', 4.2, true),
        ('junior', '2008-11-16', 6, true),
        ('junior', '2012-07-23', 4.5, true),
        ('junior', '2019-09-11', 3.7, true),
        ('junior', '2030-12-31', 0, false),
        ('adult', '2001-01-01', 8.4, true),
        ('adult', '2012-07-23', 9.9, true),
        ('adult', '2030-05-03', 0, false)
   /**/;/**/

   SELECT
        rate_value
   FROM
        labour_rate_mult
   WHERE
            rate_name = 'junior'
        AND effective_start <= '2012-07-23' -- stand in for
   CURRENT_TIMESTAMP
        AND valid
   ORDER BY
        effective_start DESC
   LIMIT 1
   /**/;/**/

Cheers.
Gavin

P.S.
Previously, I accidentally just sent it to Rich!