Set up a join logical file

These topics provide examples to illustrate how to set up a join logical file. Performance, integrity, and a summary of rules for join logical files are also included.

In general, the examples in these topics include a picture of the files, data description specifications (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 these 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.

• Basic concepts of joining two physical files (example 1)
  A join logical file is a logical file that combines (in one record format) fields from two or more physical files because in the record format not all the fields need to exist in all the physical files.
• Set up a join logical file
  This topic shows how to set up a join logical file.
• Use more than one field to join files (example 2)
  You can specify more than one join field to join a pair of files. This example shows the fields in the logical file and the two physical files.
• Read duplicate records in secondary files (example 3)
  Sometimes a join operation to a secondary file produces more than one record from the secondary file. When this occurs, specifying the JDUPSEQ keyword in the join specification for that secondary file tells the system to base the order of the duplicate records on the specified field in the secondary file.
• Use join fields whose attributes are different (example 4)
  Fields from physical files that you use as join fields generally have the same attributes (length, data type, and decimal positions). However, in some cases, the join fields might have different attributes.
• Describe fields that never appear in the record format (example 5)
  Neither fields, which (N specified in position 38) can be used in join logical file for neither input nor output, are not included in the record format. This example shows how to describe such fields that never appear in the record format.
• Specify key fields in join logical files (example 6)
  This topic discusses the rules for specifying key fields in join logical files.
• Specify select/omit statements in join logical files
  This topic discusses the rules for specifying select/omit statements in join logical files.
• Join three or more physical files (example 7)
  You can use a join logical file to join as many as 32 physical files. These files must be specified on the JFILE keyword. The first file specified on the JFILE keyword is the primary file; the other files are all secondary files.
• Join a physical file to itself (example 8)
  You can join a physical file to itself to read records that are formed by combining two or more records from the physical file itself.
• Use default data for missing records from secondary files (example 9)
  If you are joining more than two files and you specify the JDFTVAL keyword, the default value supplied by the system for a join field missing from a secondary file is used to join to other secondary files.
• A complex join logical file (example 10)
  This example shows a more complex join logical file.
• Join logical file considerations
  These topics include the performance and integrity considerations for join logical files. They also provide a summary of rules for join logical files.