Question

I have a table from our IVR that contains a unique call id, sequence number, event code, and event description. I would like to write a query that let’s me know what was the event prior to a particular event.

Answer 1

Depending on what indexes exist on the table, a straightforward inner join may receive a better-performing access plan from the query optimizer.

SELECT n.call_id, 
    n.event_dt, 
    n.sequence_number, 
    p.call_id as prior_call_id, 
    p.event_id as prior_event_id,
    p.event_dt as prior_event_dt,
    p.sequence_number as prior_sequence_number
FROM daily_events n
INNER JOIN daily_events p
    ON p.sequence_number = n.sequence_number - 1
WHERE n.event_id = '5047'
AND n.event_dt >= DATE( '01/06/2012' ) 
AND n.event_dt <= DATE( '01/07/2012' );

The query assumes that any event with a sequence number that differs by one is an appropriate match, and that the call_id doesn’t also need to match. If that assumption is incorrect,
then add AND n.call_id = p.call_id to the ON clause of the join.