Open Query File (OPNQRYF) command: Performance considerations for sort sequence tables

Here are tips and techniques for optimizing the performance of sort sequence tables.

• Grouping, joining, and selection: Open Query File (OPNQRYF) command performance
  When using an existing index, the optimizer ensures that the attributes of the selection, join, and grouping fields match the attributes of the keys in the existing index.
• Ordering: Open Query File (OPNQRYF) command performance
  For ordering fields, the optimizer is not free to use any existing access path. The sort sequence tables associated with the index and the query must match unless the optimizer chooses to do a sort to satisfy the ordering request.