Please Note: This article is written for users of the following Microsoft Excel versions: 2007, 2010, 2013, 2016, 2019, and Excel in Office 365. If you are using an earlier version (Excel 2003 or earlier), this tip may not work for you. For a version of this tip written specifically for earlier versions of Excel, click here: Ensuring Unique Values in a Column.
by Allen Wyatt
(last updated April 11, 2020)
When you are entering information in a worksheet, you may want to ensure that the data being entered is actually unique for a particular column. For instance, if you are entering a series of invoice numbers in column D of a worksheet, you may want to ensure that you don't enter the same invoice number twice.
There are a couple of ways that you can approach such a problem. If you are always entering your new information at the bottom of a column, you can use Excel's data validation feature to make sure that whatever you are entering in the current cell does not match anything higher up in the column. Simply follow these steps:
Figure 1. The Data Validation dialog box.
If you may be entering data anyplace within column D, and you want to know if you are entering a value that is elsewhere in the column (above or below the current cell), then you can follow the above steps, but use this formula in step 5:
There is one other thing to keep in mind: All bets are off if a user copies a value into a cell in the column. This results in the data validation information be overwritten as the copy is completed. If such a thing is likely to happen with your data, the only way around it is to create a macro that checks, after each action, whether the data validation has been removed from cells where it should be present. Such is not a trivial undertaking.
ExcelTips is your source for cost-effective Microsoft Excel training. This tip (10673) applies to Microsoft Excel 2007, 2010, 2013, 2016, 2019, and Excel in Office 365. You can find a version of this tip for the older menu interface of Excel here: Ensuring Unique Values in a Column.
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