sfmc-dedupe-external-rows.html

%%[
var @i, @rows, @row, @productName, @prevProductName, @rowsToReturn

set @rowsToReturn = 0 /* up to 2000 */

set @rows = LookupOrderedRows("SubscriberProducts" ,@rowsToReturn, "ProductName asc", "EmailAddress",emailaddr)

set @prevProductName = ""

for @i = 1 TO RowCount(@rows) DO

  set @row = Row(@rows,@i)
  set @ProductName = Field(@row, "ProductName")

  if empty(@prevProductName) or @productName != @prevProductName then

     set @prevProductName = @productName

]%%

     <h1>%%=v(@productName)=%%</h1>

%%[ endif ]%%

%%[ next @i ]%%