Re: Primary key data type: integer vs identity

On 4/19/19 11:32 AM, Ken Tanzer wrote:
> On Fri, Apr 19, 2019 at 11:20 AM Adrian Klaver 
> <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>> wrote:
> 
>     On 4/19/19 11:14 AM, Rich Shepard wrote:
>      > On Fri, 19 Apr 2019, Adrian Klaver wrote:
>      >
>      >> If it is working for you now I see no reason to switch.
>      >
>      > Adrian,
>      >
>      > It does work. I just learned about the SQL identity type and want
>     to learn
>      > when it's most appropriate to use. The databases I develop all
>     work with
>      > integers as primary keys and reading about the type didn't
>     clarify (for me)
>      > when it should be used.
> 
>     Mainly for folks that want cross database SQL compliance. It is not a
>     type so much as a way of specifying an auto-increment column.
> 
> 
> It also sounds like it has advantages in terms of tying your sequence 
> directly to the column.  If you drop a serial column, it doesn't drop 
> the sequence.

A serial column will:

test=> create table serial_test(id serial);
CREATE TABLE
test=> \d serial_test
                             Table "public.serial_test"
  Column |  Type   | Collation | Nullable |                 Default 

--------+---------+-----------+----------+-----------------------------------------
  id     | integer |           | not null | 
nextval('serial_test_id_seq'::regclass)

test=> select * from serial_test_id_seq ;
  last_value | log_cnt | is_called
------------+---------+-----------
           1 |       0 | f
(1 row)

test=> drop table serial_test ;
DROP TABLE 
 

test=> select * from serial_test_id_seq ; 
 

ERROR:  relation "serial_test_id_seq" does not exist 
 

LINE 1: select * from serial_test_id_seq ;

If you just use a sequence as a default value it will not  unless you 
make it OWNED by the table per the link I posted upstream.


> Once I've upgraded to 10+, I might look at converting my existing serial 
> columns.  Peter Eisentraut wrote a good piece(1) on identity columns, 
> including a function for converting existing serial columns.  I've 
> copied the function below, but had two questions about it:
> 
> 1)  Would the function as written also reassign ownership to that table 
> column?  (I see the update to pg_depend and pg_attribute, but don't know 
> enough about them to know if that changes ownership)
> 2)  Would one have to be a superuser to do this?
> 
> Thanks,
> Ken



-- 
Adrian Klaver
adrian.klaver@aklaver.com