Re: Last inserted row id with complex PK

Francisco Olarte <folarte(at)peoplecall(dot)com> writes:
> Hi Nelson:
> On Wed, Jan 8, 2014 at 4:54 PM, Nelson Green <nelsongreen84(at)gmail(dot)com> wrote:
>> I have a projects log table with a three column PK, project_num, person_num,
>> and sequence, where each new entry for a project/person combination
>> increments the sequence, which is not an auto incrementing sequence. Is
>> there any way to retrieve the last entry to the table? For instance, if the
>> last entry for person 427 on project 15 was sequence number 125, is that
>> information available to me anywhere?

> SELECT MAX(sequence) FROM project_log_table WHERE person_num=427 AND
> project_num=15

Note that this will not work terribly well if there are concurrent
insertions for the same person/project. If that's not an issue, though,
it should be fine. It may be OK even if there are sometimes concurrent
insertions, if you are prepared to retry duplicate-key failures.

> If it's a PK it should have an index and I believe it will be quite fast.

It will be fast as long as sequence is the low-order column in the index.

regards, tom lane