Re: Should I add a Index Key in this case ?

Hi Steve,
My question is should I use index on the Seat_Viewing_id ?
I have no experience in using Index hence I asked if it should be made auto-incremental?
Kindly advise how should I alter my existing table to have index. 
Tks!

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On Wednesday, October 16, 2019, 11:26 PM, Steve Midgley <science(at)misuse(dot)org> wrote:

On Wed, Oct 16, 2019 at 7:36 AM Karen Goh <karenworld(at)yahoo(dot)com> wrote:

Hi Experts,

I have a use case as follows :

 add constraints to the database so that no two reservations for the same viewing may refer to the same seat.

So, say I have a primary key like this in the table A:

    SEAT_id integer NOT NULL GENERATED ALWAYS AS IDENTITY ( INCREMENT 1 START 1 MINVALUE 1 MAXVALUE 2147483647 CACHE 1 ),
    CONSTRAINT A_pkey PRIMARY KEY (SEAT_id))
WITH (
    OIDS = FALSE
)
TABLESPACE pg_default;

So, basically I would like to create a SEAT_Viewing_Id.

In this case, do I create a Index Key or ?

How should I construct or rather alter my table A to accomodate this SEAT_Viewing_Id ?

Hope someone can tell me how.

Furthermore, whenever an insertion is done via WebApp, I would have to insert the Index key as well or does PostgreSQL will have a way to increment the Index key which is the SEAT_Viewing_Id at the same time?

Thanks & regards,
Karen

I'm not sure I understand exactly what you want to do, but it sounds like you are want to create a second field/column in your table named "SEAT_viewing_id" and you want that field to auto-increment independently from the primary key? If so, you can consider the "serial" datatype as possiblye meeting your needs: https://www.postgresql.org/docs/current/datatype-numeric.html#DATATYPE-SERIAL
So just `alter table`, to add your new field, and make its datatype `serial`.

Apologies if I misunderstood your question,Steve