March 14, 2011

SQL Server: Group By Days and Create Categories




In this post, we will see how to Group records by Days in SQL Server and then create categories. To demonstrate, we will take a sample Student-Course table where the start date and end date of each course for each student, will be recorded. We will then categorize these records by a group of days and see how many students could complete the course in the given category

Consider this table:

sqlgroupbydays

Now in order to categorize these records by days, use the following query:

groupbydate

Here’s the same query for you to try out:

DECLARE @TT Table (
CourseID int, StudentID int,
StartDt datetime, EndDt datetime
)
Insert Into @TT
SELECT 1, 1, '03/01/2011', '03/10/2011' UNION ALL
SELECT 1, 2, '03/01/2011', '03/07/2011' UNION ALL
SELECT 1, 3, '03/01/2011', '03/04/2011' UNION ALL
SELECT 2, 2, '03/01/2011', '03/11/2011' UNION ALL
SELECT 2, 4, '03/01/2011', '03/06/2011' UNION ALL
SELECT 2, 5, '03/01/2011', '03/08/2011' UNION ALL
SELECT 3, 3, '03/01/2011', '03/04/2011' UNION ALL
SELECT 3, 5, '03/01/2011', '03/05/2011' UNION ALL
SELECT 3, 6, '03/01/2011', '03/07/2011'

SELECT
CourseID,
SUM(CASE WHEN DATEDIFF(day, StartDt, EndDt)
BETWEEN 1 AND 4 THEN 1 ELSE 0 END) AS [4 or Less Days],
SUM(CASE WHEN DATEDIFF(day, StartDt, EndDt)
BETWEEN 5 AND 8 THEN 1 ELSE 0 END) AS [5 to 8 Days],
SUM(CASE WHEN DATEDIFF(day, StartDt, EndDt) > 8
THEN 1 ELSE 0 END) AS [9 or More Days]
FROM
@TT
GROUP BY CourseID

All we are doing here is using the DATEDIFF function to calculate the number of days between StartDt and EndDt and use a CASE condition to categorize records. The following output shows how many students were able to complete the course in a given range of days.

OUTPUT

image


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About The Author

Suprotim Agarwal, ASP.NET Architecture MVP works as an Architect Consultant and provides consultancy on how to design and develop Web applications.

Suprotim is also the founder and primary contributor to DevCurry, DotNetCurry and SQLServerCurry. He has also written an EBook 51 Recipes using jQuery with ASP.NET Controls.

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