A single Virtuoso procedure may produce multiple result sets, each with different result columns. A normal procedure produces one empty result set, only returning a possible return value and values of output parameters to the application.

The result_names() predefines variables to be used in a result set to follow. The variables must be previously declared, from which the column data types are ascertained. This assigns the meta data but does not send any results. The result() function sends its parameters as a single row of results. These parameters should be compatible with those in the previous result_names() . The end_results() function can be used to separate multiple result sets. The result_names() can then be used to alter the structure of the next result set.

The result_names() call can be omitted if the application already knows what columns and their types are to be returned.