Question : Grouping with DISTINCT COUNT

Hi Guys

I have made a query that can select all the mail received per day per month in a year, and it works as it should. Now i need this to support to count the number of distinct customers that receive mail per day instead of the totalt mail count.

The column is called CustomerId

How would i go by doing that here?

in the bottom you can see a select that does what i want, but i want it in my master select




/*master select*/
SELECT
      year(t1.CreatedDate) as [Year],
      month(t1.CreatedDate),
      Day1 = sum(case when day(t1.CreatedDate) = 1 then 1 else 0 end),
    Day2 = sum(case when day(t1.CreatedDate) = 2 then 1 else 0 end),
    Day3 = sum(case when day(t1.CreatedDate) = 3 then 1 else 0 end),
    Day4 = sum(case when day(t1.CreatedDate) = 4 then 1 else 0 end),
    Day5 = sum(case when day(t1.CreatedDate) = 5 then 1 else 0 end),
    Day6 = sum(case when day(t1.CreatedDate) = 6 then 1 else 0 end),
    Day7 = sum(case when day(t1.CreatedDate) = 7 then 1 else 0 end),
    Day8 = sum(case when day(t1.CreatedDate) = 8 then 1 else 0 end),
    Day9 = sum(case when day(t1.CreatedDate) = 9 then 1 else 0 end),
    Day10 = sum(case when day(t1.CreatedDate) = 10 then 1 else 0 end),
    Day11 = sum(case when day(t1.CreatedDate) = 11 then 1 else 0 end),
    Day12 = sum(case when day(t1.CreatedDate) = 12 then 1 else 0 end),
    Day13 = sum(case when day(t1.CreatedDate) = 13 then 1 else 0 end),
    Day14 = sum(case when day(t1.CreatedDate) = 14 then 1 else 0 end),
    Day15 = sum(case when day(t1.CreatedDate) = 15 then 1 else 0 end),
    Day16 = sum(case when day(t1.CreatedDate) = 16 then 1 else 0 end),
    Day17 = sum(case when day(t1.CreatedDate) = 17 then 1 else 0 end),
    Day18 = sum(case when day(t1.CreatedDate) = 18 then 1 else 0 end),
    Day19 = sum(case when day(t1.CreatedDate) = 19 then 1 else 0 end),
    Day20 = sum(case when day(t1.CreatedDate) = 20 then 1 else 0 end),
    Day21 = sum(case when day(t1.CreatedDate) = 21 then 1 else 0 end),
    Day22 = sum(case when day(t1.CreatedDate) = 22 then 1 else 0 end),
    Day23 = sum(case when day(t1.CreatedDate) = 23 then 1 else 0 end),
    Day24 = sum(case when day(t1.CreatedDate) = 24 then 1 else 0 end),
    Day25 = sum(case when day(t1.CreatedDate) = 25 then 1 else 0 end),
    Day26 = sum(case when day(t1.CreatedDate) = 26 then 1 else 0 end),
    Day27 = sum(case when day(t1.CreatedDate) = 27 then 1 else 0 end),
    Day28 = sum(case when day(t1.CreatedDate) = 28 then 1 else 0 end),
    Day29 = sum(case when day(t1.CreatedDate) = 29 then 1 else 0 end),
    Day30 = sum(case when day(t1.CreatedDate) = 30 then 1 else 0 end),
    Day31 = sum(case when day(t1.CreatedDate) = 31 then 1 else 0 end),
      
      COUNT(*) TOTAL
FROM
      MailReceived t1
WHERE
      Year(t1.CreatedDate) = 2010
GROUP BY
      year(t1.CreteadDate),
      month(t1.CreatedDate)
order by
      TOTAL DESC
















/*Customers per day*/
SELECT
      TOP 100
      convert(datetime, convert(char(10), t1.CreatedDate, 101)) thedate ,count(DISTINCT(t1.CustomerId)) Total
FROM
      MailReceived t1
WHERE
      BusinessCenterId=4
GROUP BY
      convert(datetime, convert(char(10), t1.CreatedDate, 101))
ORDER BY
      thedate desc

Answer : Grouping with DISTINCT COUNT

instead of
  Day1 = sum(case when day(t1.CreatedDate) = 1 then 1 else 0 end),
       
you want
Day1 = count(distinct case when day(t1.CreatedDate) = 1 then customerid else null end),
   
etc