You can use the floor function to cut of the time part from a date:
date(floor(MyDateTime),'DD-MM-YYYY') as MyDate
If your datetime (timestamp) field doesn't contain numeric values but text values you can use the date# function to turn the text values into dates. You'll still should use the floor function. Date(floor(date#(MyField, 'YYYYMMDD hhmmss')),'DD-MM-YYYY')
Note, all the date and timestamp formats above are just examples. Use the formats you actually need.