With Version 9 we got the ability to define a timestamp column that will automatically updated when some other column on the row is updated (kind of like a trigger).
REC_UPDT_TS TIMESTAMP NOT NULL
GENERATED BY DEFAULT
FOR EACH ROW ON UPDATE AS ROW CHANGE TIMESTAMP
However, there may be circumstances in which we don't want to have this column automatically updated. In those cases, you can code the SQL as follows;
SET column1 = 'some value'
, REC_UPDT_TS = REC_UPDT_TS
WHERE column2 = 'another value'