Here are the rules for join fields.
- Every physical file you join must be joined to another physical
file by at least one join field. A join field is a field specified as a parameter
value on the JFLD keyword in a join specification.
- Join fields (specified on the JFLD keyword) must have identical attributes
(length, data type, and decimal positions) or be redefined in the record format
of the join logical file to have the same attributes. If the join fields are
of character type, the field lengths might be different.
- Join fields need not be specified in the record format of the join logical
file (unless you must redefine one or both so that their attributes are identical).
- If you redefine a join field, you can specify N in position 38 (making
it a neither field) to prevent a program using the join logical file from
using the redefined field.
- The maximum length of fields used in joining physical files is equal to
the maximum size of keys for physical and logical files.