What Is Double Column Support?
Double column support is the ability to associate two columns (a descriptor ID column and a descriptor column) in the logical layer, and can help you to define language independent filters.
When the user creates a filter based on a descriptor column, the query tool displays a list of values to the user that are selected from the descriptor column.
This descriptor column technique is also useful when dealing with queries that involve LOB data types such as CLOBs and BLOBs and aggregate functions such as COUNT or SUM. Some data sources don't allow LOB columns to be used in the GROUP BY clause. So, instead of adding the LOB column to the GROUP BY, it's necessary to group by some other column that has a one-to-one relationship with the LOB column and then in join the LOB column after the aggregates have been computed.