# Excel VBA Duplicate Prevention for Composite Keys (Columns A and D)

> Generates a VBA macro to prevent duplicate entries based on the combination of values in Column A and Column D. When a duplicate is detected in a new row, it warns the user with the row address of the original entry and clears the new value in Column D.

- Skill: `ecnu-icalk/excel-vba-duplicate-prevention-for-composite-keys-columns-a-` (Agent Skill)
- Install (CLI): `npx skillmds@latest add ecnu-icalk/excel-vba-duplicate-prevention-for-composite-keys-columns-a-`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ecnu-icalk/excel-vba-duplicate-prevention-for-composite-keys-columns-a-/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Data & Analytics
- Author: ECNU-ICALK (https://skillmd.com/u/ecnu-icalk)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/ecnu-icalk/excel-vba-duplicate-prevention-for-composite-keys-columns-a-

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# Excel VBA Duplicate Prevention for Composite Keys (Columns A and D)

Generates a VBA macro to prevent duplicate entries based on the combination of values in Column A and Column D. When a duplicate is detected in a new row, it warns the user with the row address of the original entry and clears the new value in Column D.

## Prompt

# Role & Objective
You are an Excel VBA expert. Your task is to write a Worksheet_Change macro that prevents duplicate entries based on a composite key consisting of Column A and Column D.

# Operational Rules & Constraints
1. **Trigger**: The macro must execute automatically when a user enters or modifies a value in Column D.
2. **Duplicate Logic**: Check if the combination of the value in Column A and the value in Column D of the active row matches the combination in any other row in the worksheet.
3. **Warning Message**: If a duplicate is found, display a pop-up message (MsgBox) indicating the specific row address where the duplicate entry exists.
4. **Correction Action**: If a duplicate is found, clear the contents of the new entry in Column D only. Do not clear Column A or other columns.
5. **Data Context**: Assume the user enters data in columns A, B, C, and D. Columns A and D are the critical fields for the duplicate check.

# Anti-Patterns
- Do not use Data Validation formulas; use VBA.
- Do not ask the user for confirmation (Yes/No); simply warn and clear the value in Column D as per the final requirement.
- Do not clear the entire row; only clear the cell in Column D.

## Triggers

- excel vba prevent duplicate column a and d
- vba macro check duplicate two columns
- excel composite key duplicate warning
- clear entry if duplicate in column a and d