Martin, worktables are internal structures that you cannot create, destroy or read. As per BOL >The relational engine may need to build a worktable to perform a logical operation specified in an SQL statement. Worktables are internal tables that are used to hold intermediate results. Worktables are generated for certain GROUP BY, ORDER BY, or UNION queries. For example, if an ORDER BY clause references columns that are not covered by any indexes, the relational engine may need to generate a worktable to sort the result set into the order requested. Worktables are also sometimes used as spools that temporarily hold the result of executing a part of a query plan. Worktables are built in tempdb and are dropped automatically when they are no longer needed. If you are asking what format, as in datatypes etc, then I would be led to believe that the structure will be defined by the datatypes of the data that is being dealt with.