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Answer Posted / venkat
The format of this keyword is:
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.
Example
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
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which program rpg or cl is efficent to update a transaction onto a database file and why ?
RETRIVING DELETED RECORDS :- I'm frequently asked how to retrieve deleted records from an unjournaled physical file when the deleted records have not yet been removed from the file. Utility UNDEL lets you undelete records in a physical file. This public domain program is available in CISC and RISC versions, and the complete source code is available for download at: UNDEL for AS/400 Save File (RISC): http://www.as400network.com/sharewarefiles/undelris.zip UNDEL for AS/400 Save File (CISC): http://www.as400network.com/sharewarefiles/undel.zip UNDEL for AS/400 Save File (Source code): http://www.as400network.com/sharewarefiles/undelsrc.zip The utility takes advantage of the fact that deleted records in physical files are only flagged as deleted, and the record data still exists until it is overwritten or the file is reorganized with a utility such as RGZPFM. UNDEL simply reads the deleted record, then reuses the record by writing over it with the new record (thus eliminating the flag for the deleted record). Some homegrown and commercial utilities copy the file containing undeleted records to a save file, then use a program to read the save file, which contains live and undeleted records, to a file to undelete the records. The UNDEL utility is superior to the SAVF technique because there's no need to copy the file to a save file, which is especially important for really large files. When run, UNDEL displays the physical file records in their unformatted, raw text form. You can either position the display to a given relative record number or use F19 or F20 to find the previous and next deleted record, respectively. The utility also includes online help, which is almost unheard of for free utilities. Other utilities include the ability to undelete records. You can use the RTVDLTRCD command in the old QUSRTOOL (no longer supported by IBM). QUSRTOOL is now a commercial product called TAA Productivity Tools ( http://www.taatool.com ). The free file editor WRKDBF has a built-in undelete capability ( http://www.wrkdbf.com ), and several commercial file editors can undelete records. For a complete list of file editors, go to http://www.sourcebook400.com, select "Programmer Tools" under "Product Category," then select "File Editors."
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