IBM AS/400 manual Methods for Processing Disk Files, Limits Records, Relative Record Numbers

Methods for Processing Disk Files

Limits Records

For sequential-within-limits processing, the record-address file contains

records.			A limits record			contains		the lowest		record key	and the hig
of	the	records		in	the	file	to	be	read.
The	format		of the		limits	records in the record-address file is as
¹	The	low	key	begins in		position		1	of the	record; the high key i
	the	low	key.	No	blanks	can	appear		between	the keys.

¹Each record in the record-address file can contain only one set

record length must be greater than

or

equal

to

twice

the

length

key.

¹ The

low

key and

the

high

key in

the

limits

record

must

be

the

The

length of the

keys must

be

equal

to the length

of

the

key

be

processed.

¹ A blank entry equal

in

length

to

the

record

key

field

causes the

piler to

read

the

next

record

in

the

record-address

file.

Relative Record Numbers

For relative-record-number processing, the record-address file contains record numbers. Each record retrieved from the file being processe relative record number in the record-address file. A record-address relative record numbers cannot be used for limits processing. Each re number in the record-address file is a multi-byte binary field wher tains a relative record number.

You

can

specify

the

record-address file length

as

4,

3,

or

blank,

source

of

the

file.

When using a

record-address

file

from the

AS/4

specify

the

record-address file length as 4,

since

each

field

is

When

using

a

record-address file created for

the System/36,specifyEnvironment

the record-address file length as 3, since each field is

3

bytes

specify

the record-address file length as blank,

the compiler

will

c

record

length

at

run time and determine whether

to

treat

the

recor

3

byte

or as

4

byte.

A

minus

1

(-1

or

hexadecimal

FFFFFFFF)

relative-record-number

value

stops

use

of

a relative-record-address file record.

End

of

file

occurs w

the

record-address file have

been

processed.

Methods for Processing Disk Files

The methods of disk file processing include:

¹Consecutive processing

¹Sequential-by-key processing

¹Random-by-key processing

¹Sequential-within-limits processing.

¹Relative-record-number processing

Chapter 16. Accessing Database 291Files