A computer system executes a user-supplied query across multiple relational database tables linked by a common key. A new query form, called a composite join, takes a user-supplied query including one or more terms optionally joined by logical operations, an identification of two or more tables and an identification of a common join key shared across the tables. The composite join applies the query across the tables such that any of the query terms can be matched by any of the tables. A query is performed across all tables for each query term and any join keys associated with matching records from the tables are identified in a set of join keys associated with the respective term. The logical operations are then performed on the resulting sets of join keys to combine the results of the term queries according to the user query.