COBOL – Tricky Interview Question

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.

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32 Complex SQL queries

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How to process 2 files by comparing key field in COBOL?


First file you need to read, also read second file. If both key field matches, you 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


If both files are same number of records. It is good, our work is reduced
If T file comes to AT END you need to move HIGH VALUES into key field
If M files comes to  AT END you need to move HIGH VALUES into key field
So you 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, you can read data into local array table, and you can process the records.

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Author: Srini

Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.