Hi Experts, Well this was asked to me in an interview and I am not sure how to answer it properly : Code (Text): I have a query which is using 100 tables and multiple joins in between them, it was working fine till now but today it's started working very slow, the same query which usually takes 30-35 minutes is now taking 4-5 hours to complete. what could be the possible reason for this?? Note - All other statics like data in table, table index, load on database server etc. remains same. I have tried explaining that change in index or load on system or locking of table could be the possible reason for same, but he doesn't seems to be impressed. Can you help me to identify what else could have been checked in this scenario. Please Note - Since it's a hypothetical scenario, please don't ask me for for table schema or query being used, i just want to know the best approach that can be used in this situation.