Proposal: RETURNING primary_key()

THE ISSUE:

In JDBC there is a flag called RETURN_GENERATED_KEYS -- 
https://docs.oracle.com/javase/7/docs/api/java/sql/Statement.html#RETURN_GENERATED_KEYS

Which is left quite ambiguous, but in general it is used to return the 
"generated" Primary Key on INSERT/UPDATE/DELETE -- which is mostly 
useful in the case of INSERT, of course, as the other commands do not 
generate a key.

We can already add RETURNING after an INSERT, e.g.
  CREATE TABLE test (name TEXT, id SERIAL PRIMARY KEY);  INSERT INTO test VALUES ('PostgresQL') RETURNING id;

But the problem is that we need to know in advance the name of the "id" 
column, because if we had created the table like so:
  CREATE TABLE test (name TEXT, test_id SERIAL PRIMARY KEY);

Then we would need to use RETURNING "test_id" instead of "id".

The problem is that we do not always know in advance what the Primary 
Key is, and therefore a solution that was implemented in the pgjdbc 
driver was to append " RETURNING * " to the query, but that has its own 
problems, like returning a lot of data that is not needed, etc.  (you 
can see a longer discussion at https://github.com/pgjdbc/pgjdbc/issues/488 )


THE PROPOSAL:

The proposal is to allow something like RETURNING primary_key() (it can 
be a keyword, not necessarily a function), e.g.
  INSERT INTO test VALUES ('PostgresQL') RETURNING primary_key();

Which will return a record set according to the PRIMARY KEY that is set 
on the table.  So if the primary is "id", then you would get a column 
named "id", and if it is "test_id" you would get a column named 
"test_id" with the correct values.

If the PRIMARY KEY is made of multiple column, then all of those columns 
will be returned.

If the table does not have a PRIMARY KEY constraint then NULL will be 
returned with some arbitrary column name.

I would go further and suggest to add a function that will return the 
last primary key from a table, e.g.:
  SELECT last_primary_key() FROM test;

This of course can be beneficial for many users, and not only the JDBC 
community.

Thank you for your time and consideration,


Igal