This question you may come across in many interviews. This scenario usually comes in Banking projects/Insurance/Finance projects. You can learn domain knowledge in an easy way.
How to process 2 files by comparing key field in COBOL?
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Solution – 1 :
First file you need to read, also read second file. If both key field matches, we can ignore it. Let us say T,M files.
T < M means this is new account so we need to update in the master file
T > M means an account is missing in the Master file, so we need to update it
Solution – 2:
If both files are same number of records. It is good, our work is reduced
If T file comes to AT END we need to move HIGH VALUES into key field
If M files comes to AT END we need to move HIGH VALUES into key field
So we need to process till both key fields are equal to HIGH VALUES.
Note: Key fields must be in PIC (X) not numeric
To avoid lot of I/Os, we can read data into local array table, and we can process the records.