Use this file-level keyword to specify that records with duplicate key values are not allowed within a member of this physical or logical file.
You can specify whether null key values are to be considered as duplicates using the parameter. Any insertions or additions of new records, or updates to existing records, which might result in a duplicate key, are rejected. The application program issuing the write or the update operation receives an error message. When a workstation user is using data file utility (DFU), a message is displayed at the workstation. A copy file command that copies records with duplicate keys in this file is not completed.
UNIQUE[(*INCNULL | *EXCNULL)]The parameter is optional. When specified, it determines whether null key values cause duplicates. *INCNULL is the default and indicates to include null values when determining duplicates. *EXCNULL, when specified, indicates to exclude null values when determining duplicates.
When a logical file based on a physical file has the UNIQUE keyword, the physical file member or members cannot have duplicate key values.
When you specify the UNIQUE keyword for a physical or logical file, you must specify the MAINT(*IMMED) parameter value on the Create Physical File (CRTPF) or Create Logical File (CRTLF) command that creates the file. This means that the access path is maintained immediately when changes are made.
If you do not specify the UNIQUE keyword, records with duplicate key values are sequenced in the order you specify. If you specify the FIFO keyword, they are sequenced in first-in first-out order. If you specify the LIFO keyword, they are sequenced in last-in first-out order. If you specify the FCFO keyword, they are sequenced in first-changed first-out order. If you do not specify FIFO, LIFO or FCFO, the order in which the records are sequenced is not guaranteed.
You cannot specify the UNIQUE keyword with the FIFO, LIFO, FCFO, or REFACCPTH keywords.
The following example shows how to specify the UNIQUE keyword for a logical file.
|...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
00010A*
00020A* SAMPLE LOGICAL FILE (CUSMSTL)
00030A*
00040A UNIQUE
00050A R CUSREC PFILE(CUSMSTP)
00060A TEXT('Logical File Master Record')
00070A CUST
00080A NAME
00090A ADDR
00100A K CUST
A