Chaining in a CL Program:

Most AS/400 programmers are familiar with the Override Database File (OVRDBF) command for substituting one file for another, changing a file to share an open data path (ODP), and other common uses. But many may not be aware that it can also be used with the Receive File (RCVF) command to perform random record access, similar to CHAIN or SETLL operation codes in RPG.
The way to do this is to use the POSITION parameter of the OVRDBF command. It can be used to get a record with a certain key value. To do this, you must specify the name of a field and one of the following search values.
• KEY (Key Equal)-The record with the given key value will be retrieved.
• KEYA (Key After)-The record following the record with the given key value will be retrieved.
• KEYAE (Key After or Equal)-If a record with the given key value exists, it will be retrieved. If not, the record with the next higher value will be retrieved.
• KEYB (Key Before)-The record preceding the record with the given key value will be retrieved.
• KEYBE (Key Before or Equal)-If a record with the given key value exists, it will be retrieved. If not, the record with the next lower value will be retrieved.
The following code fragment demonstrates the use of the POSITION parameter of the OVRDBF command.

DCLF FILE(MYFILE)
OVRDBF FILE(MYFILE) +
POSITION(*KEY 1 MYFMT KEYFLD)
RCVF
This example will retrieve a record from file MYFILE (format MYFMT), which has a key value matching the value in the field KEYFLD. The other key search values work similarly.