A developer is creating a CloudPage which accepts secure parameters via an email link and will submit those parameters to another CloudPage for data upsert. The page currently captures an Appointment ID parameter passed into it and sets the value to the variable caapptld. The developer does NOT want the Appointment ID to be visible to anyone using the form.
What is the best method to ensure the parameters are passed successfully to the data upsert page?

A developer identified duplicate contacts and initiated a Contact Delete process for 10 milion subscribers. How could the process be expedited?

NTO uses data extensions to manage the subscriber information used for their email sends, and those sends includes calls to update records with new or different subscriber information. The developer handling these records writes some AMPscript to check and see if the data extension containing those records updated using an InsertDE() call if the record doesn't yet exist. Why would the developer receive an error stating the application cannot insert a duplicate value for the primary key in the data extension?

A developer needs to configure an Email Send Logging Data Extension for a new business unit. Which option should be used?

A data extension contains two fields which are being populated by a query activity. A third field has recently been added to the data extension.
Which SELECT statement is optimal for returning all of the columns in the data extension?