Re: 'Identifier' columns

David Favro wrote:
> A couple of questions about auto-assigned identifier columns,
> forgive my ignorance, I'm used to other methods to create IDs...
>
> 1. If creating a new application [i.e. no "legacy" reasons to do
> anything] using PostgreSQL 10, when creating an "auto-assigned
> integer ID" column, what are the advantages/disadvantages of using
> the 'SERIAL' datatype [or equivalent explicitly created SEQUENCE w/
> nextval() used as default for column] versus the SQL-standard
> 'integer GENERATED AS IDENTITY'? All other things being equal, it
> would seem a no-brainer to follow the standard.

Absolutely.
Use GENERATED ALWAYS AS IDENTITY.

> 2. When using the SQL-standard 'integer GENERATED AS IDENTITY'
> column, after inserting a column, what is the recommended method to
> find the ID of the just-inserted row? Is there no SQL-standard way?
> The docs seem to imply (without explicitly stating) that a SEQUENCE
> is used behind the scenes hence 'currval()' could be used, but I
> didn't see in the docs any mention of what the underlying sequence's
> name is, or how to specify a name. Perhaps 'lastval()' would work,
> but not in all cases and in any event it has a sloppy feel to me.

The best way is to use the (non-standard) RETURNING clause:

INSERT ... RETURNING id;

Yours,
Laurenz Albe
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