Prevent Duplicate Entries in Excel Using Data Validation

In this video, I’m going to show you how to prevent duplicate data entry in Excel using a column or a range of cells. The goal is to show a visual alert for the user. Duplicate data entry is not allowed.

Chapters:
00:00 Intro
00:17 Prevent Duplicate Entries Using Data Validation

How to prevent duplicate data entry in Excel:

Go to the Validation criteria group and select Custom from the drop-down list. Locate the Formula box. Type an equal sign and use the COUNTIF Formula.
Type =COUNTIF(A:A, A1)=1 The formula that I'm going to use here will be to count the values in a selected range, in this case, column A. The formula will analyze the entire range and show an error message if duplicated values are found.
To customize the error message simply jump to the Error Alert tab and add a description, like this. Click OK and add some names. I’ll try, for example, Steve. This name does not exist in the range, so I’ll continue the data entry without any error message. Let’s try Peter. Type the name and press Enter.
Excel will evaluate the formula and show an error message since the name exists in the range. The Data validation feature does not allow to enter the name again.

[Bigbear]

I am working on an asset tracker where I need to have different types of ForkLifts on their own sheet i.e. Clap, Reach, Fork, Slip that all have tablets attached to them. Is there a way to use "Data Validation =CountIF" to prevent assigning the same s/n to multiple lifts across all sheets?

[ladygj]

DOES THIS, .NO DUPLICATION' WAY WORKS FOR ROWS AS WELL?