Need to be able to define table joins explicitly #214
Description
Some analyses require reference to more than one input dataset (e.g., analysis of incidence of adverse events needs the full set of subjects from ADSL and, for example, the distinct list of SOC/PT combinations from ADAE). Although it is often possible to interpret the needs for a table join from the currently-defined metadata, it would be better to have metadata to explicitly identify required input datasets and to define the join conditions.