On Nov 15, 2011, at 15:28, Gavin Flower <gavinflo...@archidevsys.co.nz> wrote:
> On 14/11/11 18:35, Amit Dor-Shifer wrote: >> >> >> On Mon, Nov 14, 2011 at 4:29 PM, Amit Dor-Shifer <amit.dor.shi...@gmail.com> >> wrote: >> Hi, >> I've got this table: >> create table phone_calls >> ( >> start_time timestamp, >> device_id integer, >> term_status integer >> ); >> >> It describes phone call events. A 'term_status' is a sort-of an exit status >> for the call, whereby a value != 0 indicates some sort of error. >> Given that, I wish to retrieve data on devices with a persisting error on >> them, of a specific type. I.E. that their last term_status was, say 2. I'd >> like to employ some hysteresis on the query: only consider a device as >> errorring if: >> 1. the last "good" (0) term_status pre-dates a "bad" (2) term_status. >> 2. it has at least N "bad" term_status events following the last "good" one. >> 3. The time span between the first "bad" term_status event and the last one >> is >= T minutes >> >> For instance, w/the following data set: >> > Alternative thought, Have a Boolean field which is set to true for non-zero entries and false for zeros. Upon entering a zero into the table, for a given device, set all currently true records to false. Combine with a partial index on the true and you can quickly get a listing of all devices in error mode and all the recent error entries. David J.
