Re: SQL to Check whether "AN HOUR PERIOD" is between start and end timestamps

On 2009-04-02, Alvaro Herrera <alvherre@commandprompt.com> wrote:
> James Kitambara wrote:
>> Dear Srikanth,
>> You can solve your problem by doing this
>> 
>> THE SQL IS AS FOLLOWS
>>   ASSUME TIME INTERVAL 2008-12-07 07:59:59 TO 2008-12-07 08:58:59 AND THE TABLE NAME time_interval
>> 
>>  COUNT (*) FROM  
>>     (select customer_id, log_session_id, start_ts, end_ts , end_ts-start_ts as "Interval" from time_interval
>>      where end_ts-start_ts >= '1 hour'
>>      and '2008-12-07 07:59:59' between start_ts and end_ts)
>> AS COUNT ;
>
> Another way to phrase the WHERE clause is with the OVERLAPS operator,
> something like this:
>
> WHERE (start_ts, end_ts) OVERLAPS ('2008-12-07 07:59:59', '2008-12-07 08:59:59')
>
> What I'm not so sure about is how optimizable this construct is.
>

http://www.postgresql.org/docs/8.3/interactive/xindex.html
if you gave the apropriate GIST index on (start_ts, end_ts) the
overlaps may be optimisable. the subquery will run to completion 
and count will count the results. - but this form gives different results.

beter to do 

select COUNT (*) AS COUNT FROM time_interval WHERE (start_ts, end_ts) OVERLAPS ('2008-12-07 07:59:59', '2008-12-07
08:59:59')

or 
select COUNT (*) AS COUNT FROM time_interval where end_ts-start_ts >= '1 hour' and '2008-12-07 07:59:59' between
start_tsand end_ts;