1. A system for retrieving data from a plurality of data sources, said system comprising: a first data source for storing first data; a second data source for storing second data; and a server computing device in communication with the first data source and the second data source, the server computing device programmed to: receive a query execution request comprising a query definition reference and a query parameter definition, wherein the query definition reference corresponds to a query definition that includes a first query block and a second query block; create a first executable query based on the first query block and the query parameter definition; create a second executable query based on the second query block and the query parameter definition; determine an amount of data each of the first executable query and the second executable query are known to access; assign a priority level to each of the first executable query and the second executable query based on the determined amount of data each of the first executable query and the second executable query are known to access; and concurrently execute the first executable query at the first data source to create first query results and the second executable query at the second data source to create second query results based on the assigned priority level of the first executable query and the second executable query.