ENABLE Reference Manual

ENABLE FUNCTION KEYS
Key Fields
KEY FIELDS
Many of the operations that you can perform with an ENABLE
application involve entering values in key fields. Each record
in a key-sequenced file can have:
• A primary key field. The value of a primary key field
uniquely identifies a record within a file; for this reason,
an ENABLE application will not allow you to enter a value in a
primary key field if that value already exists in another
record in the file.
• Alternate key fields. The value of an alternate key field
identifies records with a certain property. Some alternate
key fields require unique values; an ENABLE application will
not allow you to enter a duplicate value in such alternate key
fields.
Each record in a relative, entry-sequenced, or unstructured file
can have:
• A courtesy key field. This key field corresponds to the
primary key field of key-sequenced files. A courtesy key
field identifies the unique record number of each record
within such files. Within these files, the record number has
the following significance:
--For relative files, the record number corresponds to the
physical position of a record within the file. The first
record position is 0, the next record position is 1, and so
forth. A record position exists whether or not a record has
been stored in that position.
--For entry-sequenced files, the record number corresponds to
the order in which a record is stored in the file. The
first record is 0, the next record is 1, and so forth.
Record numbers are always in ascending order, but the
numbering sequence is not always in steps of 1. Record 32,
for example, could be followed by record 4096. Refer to the
ENSCRIBE Programming Manual for more information.
--For unstructured files, the first record is 0, the next is
1, and so forth. The last record in the file always has the
highest record number.
• Alternate key fields. Both relative and entry-sequenced files
can have any number of alternate key fields. Alternate key
fields are not allowed for unstructured files.
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