A system and method of generating an overall top N query result from multiple sets of sessionized network events that correspond to different time periods include identifying a subset within each set of network events whose event attributes satisfy a predefined query, generating an aggregation result table for each identified subset of network events in accordance with an aggregation attribute, identifying matching first and second entries in first and second aggregation result tables that have a same aggregation attribute value, generating a new entry in a query result table by merging the matching first and second entries together, and selecting entries in the query result table that have highest session counts as the overall top N query result.