Warning when a transaction effective date matches existing row

Summary:

We would like to avoid stacked rows on employee records because it's not ideal from a reporting standpoint. Is there a way to create a warning that shows during a transaction when an effective date is selected that is already the same as an existing effective dated row on the employee's record?

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Version (include the version you are using, if applicable):

25C

Code Snippet (add any code snippets that support your topic, if applicable):