>The QUARTER() function returns the quarter. Is there a way to calculate the first and the last date of a calendar quarter? I suppose I can "build" such a function but I was wondering if there is already a "built-in" function for that?
>

No there isn't built-in function but it's easy to create an UDF

lnQuaterStart = DATE(lnYear, (lnQuarter -1) * 3 + 1, 01)
lnQuorterEnd = GOMONTH(lnQuaterStart,3) - 1