Figure A We’ll use data validation to prevent duplicate numbers in the Membership Number column. First, enter the following function into cell K3: =COUNTIF(Table1[Membership Number],B3) ...

It takes open-source data-diff only ten seconds to fully compare tables with 25M rows, and less than 5 minutes to perform the comparison for a 1-billion-row dataset – approximately the same time ...

Under the Data Tools group, click on the Data Validation option. Check the Data Validation value under the Settings tab. If the values entered there are incorrect, edit them and click OK.

Click the Data tab and in the Data Tools group, click Data Validation. In the resulting dialog, choose List from the Allow dropdown. Click inside the Source control and then highlight the Table.