Time and date dimension in data warehouse

Question

I\'m building a data warehouse. Each fact has it\'s timestamp. I need to create reports by day, month, quarter but by hours too. Looking at the examples I see that

Answer 1

My guess is that it depends on your reporting requirement. If you need need something like

WHERE "Hour" = 10

meaning every day between 10:00:00 and 10:59:59, then I would use the time dimension, because it is faster than

WHERE date_part('hour', TimeStamp) = 10  

because the date_part() function will be evaluated for every row. You should still keep the TimeStamp in the fact table in order to aggregate over boundaries of days, like in:

WHERE TimeStamp between '2010-03-22 23:30' and '2010-03-23 11:15' 

which gets awkward when using dimension fields.

Usually, time dimension has a minute resolution, so 1440 rows.