On Wed, Jan 8, 2014 at 10:22 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Francisco Olarte <folarte@peoplecall.com> writes: > Hi Nelson: > On Wed, Jan 8, 2014 at 4:54 PM, Nelson Green <nelsongreen84@gmail.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.
Concurrency is not likely to be an issue for this system, but I would certainly plan for it since I can not rule it out.
> 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.