Finding Median Between TWO Dates SQL Server 2008

I am looking of a way to take the MEDIAN of a bunch of start and end dates (LOTS AND LOTS of dates). However, it would be specific to various 'invoice numbers.' See sample data bel

Solution 1:

If you mean the set of start dates and end dates, then put them in one column:

WITH t AS (
       SELECT invoice_no, invoice_start_date, invoice_end_date, check_date, status_code,
       FROM INVOICE_HEADER INNER JOIN
            INVOICE_HEADER_CUSTOM
            ON INVOICE_HEADER.invoice_id = INVOICE_HEADER_CUSTOM.invoice_id
       WHERE status_code <> 'REJECTED' AND 
             Check_Date BETWEEN CONVERT(DATETIME, '2014-12-01 00:00:00', 102) AND
             CONVERT(DATETIME, '2014-12-31 00:00:00', 102)
     ), 
     t2 as (
      select d, row_number() over (order by d) as seqnum,
             count(*) over () as cnt
      from (select invoice_start_date as d from t
            union all
            select invoice_end_date as d from t
           ) t
     )
select dateadd(day, datediff(hour, min(d), max(d)) / 2.0, min(d))
from t2
where 2 * seqnum in (cnt, cnt + 1, cnt + 2);

Solution 2:

Ok... try something like the query on this page:

SELECT @Median = AVG(1.0 * val)
FROM 
(
  SELECT val, 
     c  = COUNT(*) OVER (),
     rn = ROW_NUMBER() OVER (ORDER BY val)
  FROM dbo.EvenRows
) AS x
WHERE rn IN ((c + 1)/2, (c + 2)/2);