A database system supporting persistent queries, using a persistent query service and various data sources. On receiving a request to create a persistent query from a client software application, the persistent query service: creates a query virtual table; parses the persistent query; creates a plurality of intermediate virtual tables; establishes listeners for the query virtual table; creates a plurality of data source virtual tables; causes the plurality of data source virtual tables to retrieve initial data from data sources; and propagates data via intermediate virtual tables to the persistent query virtual table. On detection of a data change in a data source, the associated data source virtual table causes the data change to propagate via intermediate virtual tables to the persistent query virtual table, and the client software application executes client code of at least one listener.