When I remove duplicates, it messes up the order of my table

Hi there,

I have a spreadsheet of around 10,000 customers. When I highlight the whole table and remove duplicate email addresses, it completely ruins the order of the entries. I.e. the correct customer email no longer matches with the correct customer etc.

I was under the impression when you remove a duplicate it removes that entire row of data for the area highlighted, hence everything stays in order down the sheet? Also, when you remove a duplicate, does it remove the lower of the duplicate entries or the top one?

Thanks.