added average time of process

Author: deepak14ri

BASIC JOIN/ult 1661. Average Time of Process per Machine.sql

@@ -0,0 +1,6 @@
+# Write your MySQL query statement below
+SELECT a1.machine_id, ROUND(AVG(a2.timestamp-a1.timestamp), 3) AS processing_time
+FROM Activity a1 JOIN Activity a2
+ON a1.machine_id = a2.machine_id AND a2.process_id = a2.process_id
+AND a1.activity_type = 'start' AND a2.activity_type = 'end'
+GROUP BY machine_id;