On 03/25/2015 05:25 PM, Lavrenz, Steven M wrote:
Alright everyone, this is a doozy of a problem. I am new to Postgres so I appreciate patience/understanding. I have a database of hardware objects, each of which has several different “channels”. Once per day, these channels are supposed to check in with a central server, generating an event log table (TABLE A) like the following:object_id channel check-in date **************************************** 990 1 2014-12-01 990 1 2014-12-02 990 2 2014-12-01 990 2 2014-12-02 286 2 2014-12-01 286 2 2014-12-02 286 5 2014-12-01 286 5 2014-12-02 4507 1 2014-12-01 4507 1 2014-12-02 4507 2 2014-12-01 4507 2 2014-12-02 And so on. Occasionally, communications will break down to the hardware, such that no reporting occurs. For example, let’s say that object 286 loses communications on 12/1/2014. Then the table might look like: object_id channel check-in date **************************************** 990 1 2014-12-01 990 1 2014-12-02 990 2 2014-12-01 990 2 2014-12-02 286 2 2014-12-02 286 5 2014-12-02 4507 1 2014-12-01 4507 1 2014-12-02 4507 2 2014-12-01 4507 2 2014-12-02 Or let’s say that for some reason, just channel 2 loses reporting for a day. Then we would have: object_id channel check-in date **************************************** 990 1 2014-12-01 990 1 2014-12-02 990 2 2014-12-01 990 2 2014-12-02 286 2 2014-12-02 286 5 2014-12-01 286 5 2014-12-02 4507 1 2014-12-01 4507 1 2014-12-02 4507 2 2014-12-01 4507 2 2014-12-02 I have a second table (TABLE B) with all of the object_ids and channels that are supposed to be reporting in each day. For cases where a certain channel does not check in, I want to add a column that indicates the comm failure. So, for the example where all channels on object 286 do not check in, I would like to get is something like this: object_id channel check-in date comm failure ********************************************************** 990 1 2014-12-01 No 990 1 2014-12-02 No 990 2 2014-12-01 No 990 2 2014-12-02 No 286 2 2014-12-01 Yes 286 2 2014-12-02 No 286 5 2014-12-01 Yes 286 5 2014-12-02 No 4507 1 2014-12-01 No 4507 1 2014-12-02 No 4507 2 2014-12-01 No 4507 2 2014-12-02 No I have been racking my mind for the better part of a day on how to do this. The thing is that I can do a right join of TABLE B on TABLE A, and this will populate the missing object ids and channels. However, this only works for a single day, and it gives me something like: object_id channel check-in date comm failure ********************************************************** 990 1 2014-12-01 No 990 1 2014-12-02 No 990 2 2014-12-01 No 990 2 2014-12-02 No 286 2 Yes 286 2 2014-12-02 No 286 5 Yes 286 5 2014-12-02 No 4507 1 2014-12-01 No 4507 1 2014-12-02 No 4507 2 2014-12-01 No 4507 2 2014-12-02 No I need to do a count of comm failures by day, so I need to populate the check-in date field. Please help!
Without seeing the actual query this is just a suggestion. I would say use CASE:
http://www.postgresql.org/docs/9.3/interactive/functions-conditional.html#FUNCTIONS-CASE Where if the date was not available from table A use the one from table B.
Best Regards, Steve
-- Adrian Klaver adrian.kla...@aklaver.com -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
