SQL & PL/SQL

Hi,

Another quick question if people don't mind. Bit confused about the trunc date function. I'm following the sql fundamentals exam guide and using their examples:

select trunc(to_date('02-jun-2009 13:00','dd-mon-yyyy hh24:mi')) day from dual;

this returns the 2nd of june, as it should, because, as far as i'm aware, leaving the optional variable out defaults the precision to 'day'. but when i explicitly add the variable 'day', as the guide has done with 'week' 'month' and 'year' in the following examples (so i assume this format is correct rather than dd/mon/yyyy), something goes wrong:

select trunc(to_date('02-jun-2009 13:00','dd-mon-yyyy' hh24:mi'), 'day') day from dual;

this returns the 31st of may. which is incorrect.

however replacing 'day' with 'dd' provides the correct answer of the 2nd again.

this isn't a major issue, it just bothers me that the guide seems (again) to be mistaken, something that is rapidly becoming a trend in their examples. i'd also quite like to know why this is happening, as it will help improve my understanding of sql in general - perhaps there is some sort of default to allow the correct use of the variable 'day' i'm overlooking and that the guide hasn't made clear.

btw, i'm working in sqlplus - although developer has some odd results too.

thanks alot,

nick