Making Sure Duplicate Names Aren't Entered

Using Excel for entering data is quite common. When you are entering information, you may want to limit what can be placed in a particular cell. For instance, you might be working on an employee register, and you need to make sure that you only enter each employee's name a single time in the worksheet.

One way to approach this challenge is to create a list of allowable names, either on another worksheet or in a different place on the same worksheet. Give this list of names a defined name, such as ValidNames. Then, follow these steps:

1. Choose the cells where you will be entering employee names; the ones where you want to make sure you only enter each name once. (For this example, let's assume you select cells A1:A10.)
2. Display the Data tab of the ribbon.
3. Click the Data Validation tool. Excel displays the Data Validation dialog box.
4. Make sure the Settings tab is displayed. (Click here to see a related figure.)
5. In Allow drop-down list, choose Custom.
6. In the Formula box (which appears when you complete step 4), enter the following formula:

     =AND(COUNTIF(ValidNames,A1)=1,COUNTIF($A$1:$A$10,A1)=1)

This validation formula works because it checks the input range (A1:A10) and makes sure that no more than one name from the ValidNames list appears there. There are many other variations on this particular formula that can be used, since Excel does provide many different ways to accomplish the same task. An example of an alternate formula method is provided in the Microsoft Knowledge Base:

http://support.microsoft.com/?kbid=213185

While the Knowledge Base article is specifically for Excel 2000, the formula that is at the root of the article (step 7) will work just fine in Excel 2007.