How to Efficiently Count Records Within a Specific Date Range in SQL?

Counting Records Between Two Dates

To generate a multi-axis chart, you require a count of records created for each date within a specified date range.

Problem Statement

The initial attempt at creating a query using a common table expression (CTE) faced the error "Operand type clash: datetime2 is incompatible with int." This resulted from a mismatch between the datetime2 data type used for the date range and the expected integer for the days offset.

Solution

To address this issue, a tally table or function can offer better performance. One such tally table function, created by Itzik Ben-Gan, is presented here:

WITH
    L0 AS ( SELECT 1 AS c 
            FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1),
                        (1),(1),(1),(1),(1),(1),(1),(1)) AS D(c) ),
    L1 AS ( SELECT 1 AS c FROM L0 AS A CROSS JOIN L0 AS B ),
    L2 AS ( SELECT 1 AS c FROM L1 AS A CROSS JOIN L1 AS B ),
    Nums AS ( SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS rownum
              FROM L2 )

Based on this tally table, the Date_Range_T CTE can be created:

Date_Range_T (d_range) AS (
      SELECT TOP(DATEDIFF(day, @StartDate, @EndDate) + 1)
          DATEADD(day, rownum - 1, @StartDate) AS d_range,
          DATEADD(day, rownum, @StartDate) AS d_rangeNext
      FROM Nums
    )

This Date_Range_T CTE provides the range of dates between @StartDate and @EndDate.

To calculate the count of records for each date, a query can be written as follows:

SELECT d_range, COUNT(Id) AS Total 
FROM Date_Range_T 
LEFT JOIN tbl_Support_Requests R
    ON R.CreatedDate >= T.d_range AND R.CreatedDate < T.d_rangeNext
GROUP BY d_range
ORDER BY d_range ASC

This query will return the desired result: a count of records for each date within the specified date range.

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