joining monthly values with daily values in sql - sql

Question

I have daily values in one table and monthly values in another table. I need to use the values of the monthly table and calculate them on a daily basis.
basically, monthly factor * daily factor -- for each day
thanks!
I have a table like this:
2010-12-31 00:00:00.000 28.3
2010-09-30 00:00:00.000 64.1
2010-06-30 00:00:00.000 66.15
2010-03-31 00:00:00.000 12.54
and a table like this :
2010-12-31 00:00:00.000 98.1
2010-12-30 00:00:00.000 97.61
2010-12-29 00:00:00.000 99.03
2010-12-28 00:00:00.000 97.7
2010-12-27 00:00:00.000 96.87
2010-12-23 00:00:00.000 97.44
2010-12-22 00:00:00.000 97.76
2010-12-21 00:00:00.000 96.63
2010-12-20 00:00:00.000 95.47
2010-12-17 00:00:00.000 95.2
2010-12-16 00:00:00.000 94.84
2010-12-15 00:00:00.000 94.8
2010-12-14 00:00:00.000 94.1
2010-12-13 00:00:00.000 93.88
2010-12-10 00:00:00.000 93.04
2010-12-09 00:00:00.000 91.07
2010-12-08 00:00:00.000 90.89
2010-12-07 00:00:00.000 92.72
2010-12-06 00:00:00.000 93.05
2010-12-03 00:00:00.000 91.74
2010-12-02 00:00:00.000 90.74
2010-12-01 00:00:00.000 90.25
I need to take the value for the quarter and multiply it buy all the days in the quarter by the daily value

Answer 1

You could try:
SELECT dt.day, dt.factor*mt.factor AS daily_factor
FROM daily_table dt INNER JOIN month_table mt
ON YEAR(dt.day) = YEAR(mt.day)
AND FLOOR((MONTH(dt.day)-1)/3) = FLOOR((MONTH(mt.day)-1)/3)
ORDER BY dt.day
or (as suggested by #Andriy)
SELECT dt.day, dt.factor*mt.factor AS daily_factor
FROM daily_table dt INNER JOIN month_table mt
ON YEAR(dt.day) = YEAR(mt.day)
AND DATEPART(QUARTER, dt.day) = DATEPART(QUARTER, mt.day)
ORDER BY dt.day