You can clear the contents, as well as the formatting of cells.
Prerequisite
A table view is created for the query or the ad-hoc analysis.
Procedure
Start the query or the ad-hoc analysis.
Click Output if the table is hidden.
Activate the Spreadsheet tab bar.
Select the cells whose formats you want to clear.
Click Delete > Clear formatting and contents.
You have cleared the contents, as well as the formatting of the cells.