Jochen, also I would like to mention two things.
First, you did not make a mistake. Non-integer numbers are not allowed in “Select matching DB rows” and “Delete matching DB rows” actions in order not to deal with the comparison of floating-point numbers.
Second, when a datetime value is exported to EasyMorph from a database, its fractional seconds part is truncated to 3 digits. For instance,
So if your datetime values have seconds with more than 3 fractional digits, you have to wrap the datetime column from the Target_Table with a CAST expression which truncates column values to only 3 fractional digits. Otherwise the original database timestamps won’t match (i.e. be equal to) the timestamps imported from EasyMorph.
I can send you the exact CASE expression if you can tell me which database you are using.