The Open Query File (OPNQRYF) command uses the same database support as logical files and join logical files. Therefore, the performance of functions like building a keyed access path or doing a join operation is the same.
The selection functions done by the OPNQRYF command (for the QRYSLT and GRPSLT parameters) are similar to logical file select/omit. The main difference is that for the OPNQRYF command, the system decides whether to use access path selection or dynamic selection (similar to omitting or specifying the DYNSLT keyword in the DDS for a logical file), as a result of the access paths available on the system and what value was specified on the OPTIMIZE parameter.