Re: How do I enabled Windows 10 to be able to run PSQL etc

On Thu, Sep 12, 2019 at 11:50 AM Karen Goh <karenworld(at)yahoo(dot)com> wrote:

> Anyway, now my problem is that i get a
>
> org.postgresql.util.PSQLException: ERROR: null value in column "parent_id"
> violates not-null constraint
>
> I'd like to know since I have already made parent_id a primary key, do I
> need to put a idenity as ALWAYS and increment by 1 ?
>
> cos another table I had used pgAdmin4 to define it as identity, ALWAYS,
> increment 1 and it works well....
>
> so what is the difference between identity and PRIMARY KEY ?
>
> and if I follow the other table definition for id and put in the ALWAYS,
> it will give me another problem...that the generated_id doesn't get
> inserted even though it should not
>

Hi Karen,

Please bottom post on this forum - it's uncommon these days, but the custom
on this email list to post replies at the bottom of the email.

Regarding your question about nulls and primary keys -- yes you want to
define, where it makes sense, to use autoincrementing primary keys, if you
want the system to manage your keys. Note that autoincrementing IDs, if
exposed to the public via the web or similar, could create some security
issues.

But in many cases it makes a lot of sense to use them. To create a primary
key that autoincrements, use the "serial" or "bigserial" datatype. Combined
with a primary key (that enforces "not null" among other things), your
create table would look like this:

CREATE TABLE sample (
id SERIAL PRIMARY KEY,);

I have not tested it, but I'd guess you should be able to alter a
table that has an integer primary key and convert it to a serial. I
hope that's helpful! Steve