IBM AS/400 manual Example of Random-by-Key Processing, Methods for Processing Disk Files

Methods for Processing Disk Files

Random-by-Key Processing

For the random-by-key	method of		processing, a search argument		that	id
key of the record	to be	read is		specified in factor 1 of the
for the CHAIN operation. Figure 151 on				page 300 shows an example of a
externally described	DISK	file	being	processed randomly by	key.	The

record can be read from the file either during detail calculations culations.

The random-by-key method of processing is valid for a full procedural nated as an input file or an update file.

For an externally described file, position 34 of the file descripti contain a K, which indicates that the file is processed according that is built on keys.

The

data description

specifications (DDS)

for the file

specifies

th

the key value (the key

field).

Position

35

of

the

file description

blank.

A program-described file

must

be

designated

as

an

indexed

file

(I

and

position 34 of

the

file

description

specification

must

contain

a

Z. The length		of	the	key	field is identified in positions 29-33 of
specification,		and	the	starting		location	of the	key field is specif
keyword.	Data description specifications must be							used	to	create th
a program	described input				file	(see	“Indexed	File”	on	page 288).

Example of Random-by-Key Processing

The following is an example of how to use the random-by-key method o essing data. Figure 144 on page 294 and Figure 150 show the data de specifications (DDS) for the physical files used by EMSTUPD ( Figure page 300).

A*****************************************************************

A*	RELATED PGMS:	EMSTUPD						*
A*	DESCRIPTIONS:	This	is the	DDS	for the physical		file CHANGE. *
A*		It contains		one	record	format called CHGREC.		*
A*		This	file contains new			data that	is used to	*
A*		update the EMPMST file.						*

A*****************************************************************

A*

AR CHGREC

A	ENUM	5	0	TEXT('EMPLOYEE NUMBER')
A	NNAME	20		TEXT('NEW NAME')
A	NTYPE	1		TEXT('NEW TYPE')
A	NDEPT	3	0	TEXT('NEW	DEPARTMENT')
A	NNHRS	3	1	TEXT('NEW	NORMAL WEEK HOURS')

AK ENUM

Figure 150.		DDS for database file CHANGE (physical file)
EXAMPLE	PROGRAM:			In this example, the	EMPMST file is	defined	as an
Full-Procedural			file.	The update file CHANGE is to be		processed by ke
for	each	of	the	externally described	files (EMPMST	and CHANGE)	identif

ENUM field as the key field. The read/update processes are all co operations specified in the Calculation Specifications.

Chapter 16. Accessing Database 299Files