Join Logical File Considerations

This section covers the following topics:

• Basic concepts of joining two physical files (Example 1)
• Setting up a join logical file
• Using more than one field to join files (Example 2)
• Handling duplicate records in secondary files using the JDUPSEQ keyword (Example 3)
• Handling join fields whose attributes do not match (Example 4)
• Using fields that never appear in the record format to join files--neither fields (Example 5)
• Specifying key fields in join logical files (Example 6)
• Specifying select/omit statements in join logical files
• Joining three or more physical files (Example 7)
• Joining a physical file to itself (Example 8)
• Using default data for records missing from secondary files--the JDFTVAL keyword (Example 9)
• Describing a complex join logical file (Example 10)
• Performance considerations
• Data integrity considerations
• Summary of rules for join logical files

In general, the examples in this section include a picture of the files, DDS for the files, and sample data. For Example 1, several cases are given that show how to join files in different situations (when data in the physical files varies).

In the examples, for convenience and ease of recognition, join logical files are shown with the label JLF, and physical files are illustrated with the labels PF1, PF2, PF3, and so forth.