Recently I have answered one of the SQL-based questions in the CodeProject. Thanks for the participant that question wake up me to write this blog post.
Question:
He has a table (tblLeave) with the data like below.
PAYCODE LV_TYPE FROM_DATE TO_DATE LVALUE 5023 SL 14/12/2012 0:00 14/12/2012 0:00 1 5023 SL 15/12/2012 0:00 15/12/2012 0:00 1 5023 COF 16/12/2012 0:00 16/12/2012 0:00 1 5023 SL 19/12/2012 0:00 19/12/2012 0:00 1 5023 SL 22/12/2012 0:00 22/12/2012 0:00 1 5023 SL 23/12/2012 0:00 23/12/2012 0:00 1 5023 SL 24/12/2012 0:00 24/12/2012 0:00 1 5023 PL 28/12/2012 0:00 28/12/2012 0:00 1 5023 PL 29/12/2012 0:00 29/12/2012 0:00 1 5023 PL 30/12/2012 0:00 30/12/2012 0:00 1 5023 PL 31/12/2012 0:00 31/12/2012 0:00 1
Moreover, he wants to output the data as below
PAYCODE LV_TYPE FROM_DATE TO_DATE LVALUE 5023 SL 14/12/2012 0:00 15/12/2012 0:00 2 5023 COF 16/12/2012 0:00 16/12/2012 0:00 1 5023 SL 19/12/2012 0:00 19/12/2012 0:00 1 5023 SL 22/12/2012 0:00 24/12/2012 0:00 3 5023 PL 28/12/2012 0:00 31/12/2012 0:00 4
Condition: If the same type of leave taken continuously, it should be merged in one row mentioning from_date to to_date.
Answer:
When I saw that question the first time, I did not go through in details and just thought that was an easy grouping query. And I just gave following answer.
SELECT LV_TYPE,LV_TYPE,MIN(FROM_DATE) AS FROM_DATE ,MAX(TO_DATE) AS TO_DATE, COUNT(LVALUEP) AS LVALUE FROM tblLeave GROUP BY PAYCODE,LV_TYPE
However, that is wrong, he made comments saying it does not make sense and highlighted the condition he wants. (Thanks to him; he did not down vote my answer). Again I read the question… Oh… That was a tricky question. He needs to group the leave by consecutive date. Isn’t that tricky?
To answer that, I use the DATEDIFF SQL function
DATEDIFF ( datepart , startdate , enddate )
http://msdn.microsoft.com/en-us/library/ms189794.aspx
Following is my answer and the output
SELECT PAYCODE,LV_TYPE, MIN(FROM_DATE) AS FROM_DATE,
MAX(FROM_DATE) AS TO_DATE, COUNT('A') AS LVALUE
FROM (
SELECT PAYCODE,LV_TYPE,FROM_DATE,
DATEDIFF(D, ROW_NUMBER() OVER(ORDER BY FROM_DATE), FROM_DATE) AS Diff
FROM tblLeave) AS dt
GROUP BY PAYCODE,LV_TYPE, Diff
ORDER BY FROM_DATE
PAYCODE LV_TYPE FROM_DATE TO_DATE LVALUE ----------- ------- ----------------------- ----------------------- ----------- 5023 SL 2012-12-14 00:00:00.000 2012-12-15 00:00:00.000 2 5023 COF 2012-12-16 00:00:00.000 2012-12-16 00:00:00.000 1 5023 SL 2012-12-19 00:00:00.000 2012-12-19 00:00:00.000 1 5023 SL 2012-12-22 00:00:00.000 2012-12-24 00:00:00.000 3 5023 PL 2012-12-28 00:00:00.000 2012-12-31 00:00:00.000 4
Query Explanation:
Before explaining the logic see the following query and the output.
SELECT PAYCODE,LV_TYPE,FROM_DATE,
ROW_NUMBER() OVER(ORDER BY FROM_DATE) AS ROW_NUMBER,
DATEDIFF(D, ROW_NUMBER() OVER(ORDER BY FROM_DATE), FROM_DATE) AS Diff
FROM tblLeave
PAYCODE LV_TYPE FROM_DATE ROW_NUMBER Diff ----------- ------- ----------------------- -------------------- ----------- 5023 SL 2012-12-14 00:00:00.000 1 41254 5023 SL 2012-12-15 00:00:00.000 2 41254 5023 COF 2012-12-16 00:00:00.000 3 41254 5023 SL 2012-12-19 00:00:00.000 4 41256 5023 SL 2012-12-22 00:00:00.000 5 41258 5023 SL 2012-12-23 00:00:00.000 6 41258 5023 SL 2012-12-24 00:00:00.000 7 41258 5023 PL 2012-12-28 00:00:00.000 8 41261 5023 PL 2012-12-29 00:00:00.000 9 41261 5023 PL 2012-12-30 00:00:00.000 10 41261 5023 PL 2012-12-31 00:00:00.000 11 41261
By seen this, you will realize that above query generate the same Diff value for all the consecutive dates. Now you can easily group this and get the counts as you like.
Filed under: CodeProject, SQL Tagged: ASP.Net, C#, computer, language text, SQL 2005, SQL 2008, SQL 2012, SQL Server, technology Image may be NSFW.
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