Here’s all about access modes in VSAM file. Those are sequential, random and dynamic reads. When to use , in COBOL’ explained in this article.
VSAM File Access Modes
Only sequentially you can read. First you need to give START command to establish a key. Then READ NEXT to get next record and so on.
START file-name KEY IS EQUAL TO ALTERNATE-RECORD-KEY
You can go to any key either forward way or backward way.
- You can read a record Sequentially and also you can read random record. When a direct READ is performed for a VSAM indexed file, based on an alternate index for which duplicates exist, only the first record in the data set (base cluster) with that alternate key value is retrieved.
- You need a series of READ NEXT statements to retrieve each of the data set records with the same alternate key.
File status codes
A file status code of 02 is returned if there are more records with the same alternate key value to be read; a code of 00 is returned when the last record with that key value has been read.