SQL Write a query to find out what was the average # of events in sessions with a purchase?

A session is a user's trip, their entire trip, to the website, and it typically includes multiple events. Sessions WITH a purchase have a user$\_$id$.$ Sessions WITHOUT a purchase do not.

Tabel contains the following column

EVENT$\_$ID NUMBER$(38,0)$

EVENT$\_$TYPE VARCHAR $(16777216)$

SESSION$\_$ID $(16777216)$

SESSION$\_$SEQUENCE NUMBER $(38,0)$

TIMESTAMP VARCHAR $(16777216)$

USER$\_$ID NUMBER$(38,0)$

IP$\_$ADDRESS VARCHAR $(16777216)$

BROWSER VARCHAR $(16777216)$

TRAFFIC$\_$ SOURCE VARCHAR $(16777216)$

SOURCE VARCHAR $(16777216)$

URI VARCHAR $(16777216)$

CITY VARCHAR $(16777216)$

STATE VARCHAR $(16777216)$