The DATA_LENGTH column in USER_/ALL_/DBA_TAB_COLUMNS is more or less meaningless for views - in particular for DATE datatype. It doesn't tell you anything since view is only a stored query.

FYI, as soon as you perform any DATE operation on DATE datatype in view (apply any kind of DATE functions, perform any date arythmetics) the DATA_LENGTH will show 8 bytes - so it's not only with TRUNC() function.

Abyway, to understand where that 8th byte came from, check the following thread (in particular on page 2): http://www.dbasupport.com/forums/sho...threadid=16402