On 3/7/2016 1:20 PM, Tom Lane wrote:


Yeah.  I'm rather suspicious of this proposal; I do not think it's
actually very useful to return a primary-key value without any indication
of what the primary key is.  There are also corner cases where it seems
pretty ill-defined.  For example, suppose you do this on an inheritance
parent table that has a pkey defined, but not all its child tables do
(or maybe they do but their pkeys aren't identical to the parent's).
What should happen then?
First, thank you for your reply. I appreciate it. I do not know the answer to that question.

That's an exceptionally weak use-case to argue for this with.  Unless
you can get *all* those DBMS suppliers to invent equivalent features,
you're going to have to have pkey-querying logic anyway.  The argument
for bespoke syntax for it in just one DBMS seems pretty weak.
Fair enough, but my idea was that this will be used by the JDBC driver in this case. The other DBMS suppliers have their JDBC driver return a value, usually it is SERIAL type. But there is no standard for the column name. In SQL Server, for example, it is IDENTITYCOL while in MySQL it is GENERATED_KEY.

The thing is that in SQL Server I can do, for example, "SELECT @@identity" and get the last value that was inserted. In SQL Server, however, Microsoft took the easy way and enforced only a single auto-generated identity column per table. The closest thing I can do in PostgreSQL is "SELECT lastval()" but what if there are multiple sequences in that table?
I am fairly sure, also, that all of those systems have support for the
SQL-standard information_schema views.  So if you write a pkey-identifying
query against those views, you'd have some chance of a solution that
actually did work everywhere.
The other JDBC drivers return the last SERIAL value from the table that had the insert, so there's no issue there. Querying the information_schema views with each INSERT will probably cause a major performance hit.

Anyway, I trust that you know much more about databases than I do, so if you don't think that it's a good idea, I accept that.

Best,


Igal


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