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Prevent/Stop Duplicates in Excel

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Data Validation to Stop/Prevent Excel Duplicates

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Stop/Prevent Duplicates in Excel Download a Workbook Showing Data Validation

If you are familiar with the Excel Data Validation feature, we can move into a great use for it! That is, prevent duplicates in an Excel Spreadsheet.

Let us assume the range we want to prevent duplicates in is the range A1:A100.

1) Select range A1:A100 Starting from A1. This will ensure the active cell is A1

2) Go to Data>Validation and choose "Custom" from the "Allow:" box on the "Settings" page.

3) In the box below type the formula as show below;

=COUNTIF($A$1:$A$100,A1)=1

4) Optional: Click the "Input Message" page tab and enter a message that the users sees each time they select any cell that has this Validation applied.

5) Optional: Click the "Error Alert" page tab and set the level according to the list below

a) Stop: No user will be allowed to enter data that already exists. They will have the choice to Retry or Cancel.

b) Warning: User will be allowed to enter data that already exists, but only after confirming the entry by clicking "Yes" on the message box they are shown when entering duplicate data. The default button is the "No" button and they also have the choice of clicking "Cancel"

c) Information: User will be allowed to enter duplicates after confirming the entry by clicking "OK" on the message box they are shown when entering duplicate data. The default button is the "OK" button and they also have the choice of clicking "Cancel".

Once we have done this, we simply click OK and we are done. Now test it by entering duplicate data.

Now, it is not possible to enter the same data twice in the range A1:A100. It is important to note the Absolute of $A$1:$A$100 in the COUNTIF function and that the single reference (A1) is a Relative reference. This is why step 1 states to Start from A1 (in this case) ensuring A1 becomes the active cell. The COUNTIF formula in the Data Validation for A2 will change automatically to;

=COUNTIF($A$1:$A$100,A2)>1

Note the $A$1:$A$100 never changes due to the use of Absolute on both the column ("A") and the rows (1:100). Download a Workbook Showing Data Validation

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