I am aware of SLA functionality at high level .I want to understand in detail like what happens when a sla agent triggers, when it pick and process the cases. How the data in Pc_assigntable and sla tables are related and does SLA agent delete the value of field pxrefqueuekey in assign table once the goal time is reached.
SLA agent would run typically for every 30 sec and would search for queue entry. If there are queue entry corresponding to an assignment it would get processed. Tracing the agent would help you to understand more on from which rule it starts and where it ends.
The blob column in pr_sysqueue_sla table will have info on which assignment the queue entry belongs to and thus sla and assing table are related.