In many ways, reading through a logical file & OPNQRYF perform about the same. OPNQRYF extends beyond the capabilities of doing I/O through a logical file by providing the ability to do dynamic record selection, mapped fields, dynamic join, record aggregation, and other database functions.
If you're just starting to explore the use of the OPNQRYF statement, then it might also be a good time to look at embedding SQL statements in your RPG programs to perform dynamic selection, join, aggregation, etc. This recommendation is based on the fact that SQL is strategic interface for database access on iSeries servers.
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This was first published in February 2003