Question

I have specific date range like

From Date        To Date
---------------------------    
2012-11-10       2012-11-15
2012-11-21       2012-11-22
2012-11-30       2012-12-01

I want to write a SQL query which calculates the total no of days between two dates and sum total number of days of particular month

The output I wanted is,

No of days     month
--------------------
   9            11
   1            12

Can anyone help me to write this SQL query?

Answer 1

Ideally, you have a table named “Dates” with all the dates you will ever use, e.g. year 1950 through 2100. This query will give you the result you want:

  select dateadd(m,datediff(m, 0, d.thedate),0) themonth, count(1)
    from dates d
    join ranges r on d.thedate between r.[from date] and r.[to date]
group by datediff(m, 0, d.thedate)
order by themonth;

Result:

|   themonth | COLUMN_1 |
-------------------------
| 2012-11-01 |        9 |
| 2012-12-01 |        1 |

Note that instead of just showing “11” or “12” as month, which doesn’t work well if you have ranges going above 12 months, or doesn’t help sorting when it crosses a new year, this query shows the first day of the month instead.

If not, you can virtually create a dates table on the fly, per the expanded query below:

;with dates(thedate) as (
  select dateadd(yy,years.number,0)+days.number
    from master..spt_values years
    join master..spt_values days
      on days.type='p' and days.number < datepart(dy,dateadd(yy,years.number+1,0)-1)
   where years.type='p' and years.number between 100 and 150
      -- note: 100-150 creates dates in the year range 2000-2050
      --       adjust as required
)
  select dateadd(m,datediff(m, 0, d.thedate),0) themonth, count(1)
    from dates d
    join ranges r on d.thedate between r.[from date] and r.[to date]
group by datediff(m, 0, d.thedate)
order by themonth;

The full working sample is given here: SQL Fiddle