If you access a logical file (or physical with key) sequentially, the reading of the file is performed according to the writing sequence of the records in the physical file.
To read the logical or physical file in key sequence, you must:
define a view with an access by key,
define at least one access path field (even if it seems useless).
Example
Reading the complete "sales" file by customer_code.
Defining the view for the "sales" file per key.
Guide word: R_SALES
READ R_SALES
DO_WHILE R_SALES EXISTS
...
READ R_SALES
REDO
Note: If you use the IBM command OPNQRYF, you must create a view that uses sequential access, except for some particular cases; for further details on this subject, see the "Programming Control Language Reference" volume 4 (IBM manual SC21-9778-2).