Assume that do you want to restrict the duplicate value in A to C Column then
use this formula in Validation.
Place the cursor in A1 cell and press Cntrl+Spacebar which will select the A
Column and hold the shift key and extend the selection up to C Column by
using right arrow (i.e. A to C)
Note that the Active cell should be A1 since the below formula refers the A1
cell. Active cell will have the white background after selection also.
Select Data>>Validation>>Settings>>Allow>>(select) Custom>>Formula (paste
the below formula)
=COUNTIF(A:C,A1)<2
Select Data>>Validation>>Error Alert>>Title type “This No is already pickedâ€
In Error Message>> type “Trying to create Duplicate Record†or your desired
Error Message.
Give ok.
Change the cell reference A:C & A1 to your desired cell, if required
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