FinanceTier 1212 minintermediate

Block Duplicate Transaction IDs

Use a custom formula validation rule so the same transaction ID can never be entered twice.

What you will learn

• Write a custom data validation formula using COUNTIF
• Explain why a fixed list cannot stop a duplicate entry
• Apply a validation rule to a whole column rather than one cell

Excel skills

Data Validation - Custom Formula · Data Validation

The task

Transaction IDs in column A must be unique - the same ID entered twice would let one transaction be recorded as two. Add a custom data validation rule to column A that rejects any ID already used elsewhere in the column.

You work in a real spreadsheet in your browser, and your answer is checked against hidden traps the moment you submit.

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