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yogi123
Posted Wednesday, October 10, 2012 1:20 PM
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Hello Everyone

I Have one task, in that there are two tables,
one has student testing dates
and other has student enrollment dates.

CREATE TABLE #TestDates
(
	iSchoolYearCode int NOT NULL,
	dtStartDate DATETIME NOT NULL
)


insert into #TestDates values (2011,'2011-08-22 00:00:00.000')
insert into #TestDates values (2011,'2011-12-14 00:00:00.000')
insert into #TestDates values (2011,'2012-05-01 00:00:00.000')
insert into #TestDates values (2012,'2012-08-30 00:00:00.000')


This tables has students Test Dates.

CREATE TABLE #EnrollmentDates
(
	iSchoolYearCode int NOT NULL,
	dtRunDate DATETIME NOT NULL
)

insert into #EnrollmentDates values (2011,'2011-06-16 06:00:06.780')
insert into #EnrollmentDates values (2011,'2011-10-14 11:43:48.840')
insert into #EnrollmentDates values (2011,'2011-11-01 06:00:05.353')
insert into #EnrollmentDates values (2011,'2011-12-03 06:00:06.980')
insert into #EnrollmentDates values (2011,'2012-01-11 06:00:06.947')
insert into #EnrollmentDates values (2011,'2012-01-28 06:00:06.733')
insert into #EnrollmentDates values (2011,'2012-02-11 06:00:07.130')
insert into #EnrollmentDates values (2011,'2012-03-10 06:00:09.083')
insert into #EnrollmentDates values (2011,'2012-04-14 06:00:08.330')
insert into #EnrollmentDates values (2011,'2012-05-12 06:00:11.163')
insert into #EnrollmentDates values (2011,'2012-06-14 06:00:07.893')
insert into #EnrollmentDates values (2012,'2012-10-08 23:47:43.897')


This tables has students Enrollment Dates.

I need to display most nearest Enrollment Dates with respect to Test dates

something link this 

dtStartDate			dtRunDate
2011-08-22 00:00:00.000		2011-06-16 06:00:06.780
2011-12-14 00:00:00.000		2011-12-03 06:00:06.980
2012-05-01 00:00:00.000		2012-04-14 06:00:08.330
2012-08-30 00:00:00.000		2012-06-14 06:00:07.893


Please help me to build the logic for this

Thanks
Post #1371090
Sean Lange
Posted Wednesday, October 10, 2012 1:52 PM


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This looks a lot like homework. We don't typically provide answers for homework because we want you to learn.

However, it seems you want the most recent date prior to the test date for each value in the test table?

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Post #1371101
yogi123
Posted Wednesday, October 10, 2012 1:55 PM
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Sean Lange (10/10/2012)
This looks a lot like homework. We don't typically provide answers for homework because we want you to learn.

However, it seems you want the most recent date prior to the test date for each value in the test table?


This is not Homework. I have task in that i need to use this logic.

and You correct I need most recent date prior to the test date.

I am thinking to do with cursor, what you say?
Post #1371102
Sean Lange
Posted Wednesday, October 10, 2012 2:03 PM


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yogi123 (10/10/2012)
Sean Lange (10/10/2012)
This looks a lot like homework. We don't typically provide answers for homework because we want you to learn.

However, it seems you want the most recent date prior to the test date for each value in the test table?


This is not Homework. I have task in that i need to use this logic.

and You correct I need most recent date prior to the test date.

I am thinking to do with cursor, what you say?


No you certainly don't need a cursor for this. Cursors are very rarely required for data manipulation. They are very resource intensive and can be huge issue for performance.

I can think of two ways to do this immediately without a cursor. I am sure there are other ways to do this.

The first is an inline subquery. 
select *, (select top 1 dtRunDate from #EnrollmentDates where dtRunDate <= #TestDates.dtStartDate order by dtRunDate desc) as dtRunDate
from #TestDates

The second uses Apply as a correlated subquery.
select *
from #TestDates
outer apply (select top 1 dtRunDate from #EnrollmentDates where dtRunDate <= #TestDates.dtStartDate order by dtRunDate desc) x

The second approach will produce a slightly simpler execution plan. You need to make sure you understand the logic of either approach.

BTW, excellent job posting ddl and sample data. I wish more people would post things so nicely. It really makes it easy for us to help.

_______________________________________________________________

Need help? Help us help you.

Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.

Need to split a string? Try Jeff Moden's splitter.

Cross Tabs and Pivots, Part 1 – Converting Rows to Columns
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs
Post #1371108
yogi123
Posted Wednesday, October 10, 2012 2:05 PM
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Sean Lange (10/10/2012)
yogi123 (10/10/2012)
Sean Lange (10/10/2012)
This looks a lot like homework. We don't typically provide answers for homework because we want you to learn.

However, it seems you want the most recent date prior to the test date for each value in the test table?


This is not Homework. I have task in that i need to use this logic.

and You correct I need most recent date prior to the test date.

I am thinking to do with cursor, what you say?


No you certainly don't need a cursor for this. Cursors are very rarely required for data manipulation. They are very resource intensive and can be huge issue for performance.

I can think of two ways to do this immediately without a cursor. I am sure there are other ways to do this.

The first is an inline subquery. 
select *, (select top 1 dtRunDate from #EnrollmentDates where dtRunDate <= #TestDates.dtStartDate order by dtRunDate desc) as dtRunDate
from #TestDates

The second uses Apply as a correlated subquery.
select *
from #TestDates
outer apply (select top 1 dtRunDate from #EnrollmentDates where dtRunDate <= #TestDates.dtStartDate order by dtRunDate desc) x

The second approach will produce a slightly simpler execution plan. You need to make sure you understand the logic of either approach.

BTW, excellent job posting ddl and sample data. I wish more people would post things so nicely. It really makes it easy for us to help.



Thank You so much
Post #1371109
Alan.B
Posted Wednesday, October 10, 2012 2:52 PM


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yogi123 (10/10/2012)
Hello Everyone

I Have one task, in that there are two tables,
one has student testing dates
and other has student enrollment dates.

CREATE TABLE #TestDates
(
	iSchoolYearCode int NOT NULL,
	dtStartDate DATETIME NOT NULL
)


insert into #TestDates values (2011,'2011-08-22 00:00:00.000')
insert into #TestDates values (2011,'2011-12-14 00:00:00.000')
insert into #TestDates values (2011,'2012-05-01 00:00:00.000')
insert into #TestDates values (2012,'2012-08-30 00:00:00.000')


This tables has students Test Dates.

CREATE TABLE #EnrollmentDates
(
	iSchoolYearCode int NOT NULL,
	dtRunDate DATETIME NOT NULL
)

insert into #EnrollmentDates values (2011,'2011-06-16 06:00:06.780')
insert into #EnrollmentDates values (2011,'2011-10-14 11:43:48.840')
insert into #EnrollmentDates values (2011,'2011-11-01 06:00:05.353')
insert into #EnrollmentDates values (2011,'2011-12-03 06:00:06.980')
insert into #EnrollmentDates values (2011,'2012-01-11 06:00:06.947')
insert into #EnrollmentDates values (2011,'2012-01-28 06:00:06.733')
insert into #EnrollmentDates values (2011,'2012-02-11 06:00:07.130')
insert into #EnrollmentDates values (2011,'2012-03-10 06:00:09.083')
insert into #EnrollmentDates values (2011,'2012-04-14 06:00:08.330')
insert into #EnrollmentDates values (2011,'2012-05-12 06:00:11.163')
insert into #EnrollmentDates values (2011,'2012-06-14 06:00:07.893')
insert into #EnrollmentDates values (2012,'2012-10-08 23:47:43.897')


This tables has students Enrollment Dates.

I need to display most nearest Enrollment Dates with respect to Test dates

something link this 

dtStartDate			dtRunDate
2011-08-22 00:00:00.000		2011-06-16 06:00:06.780
2011-12-14 00:00:00.000		2011-12-03 06:00:06.980
2012-05-01 00:00:00.000		2012-04-14 06:00:08.330
2012-08-30 00:00:00.000		2012-06-14 06:00:07.893


Please help me to build the logic for this

Thanks


This is what I came up with...

WITH dt AS
(
	SELECT	DENSE_RANK() OVER (ORDER BY tdt.dtStartDate) x,
			tdt.dtStartDate,
			edt.dtRunDate
	FROM #TestDates tdt
	CROSS JOIN #EnrollmentDates edt 
	WHERE tdt.dtStartDate > edt.dtRunDate
),
maxSDt AS
(
	SELECT DISTINCT x,
			MAX(dtStartDate) OVER (PARTITION BY x) y
	FROM dt
),
maxRDt AS
(
	SELECT DISTINCT x,
			MAX(dtRunDate) OVER (PARTITION BY x) y
	FROM dt
)
SELECT	SDt.y dtStartDate,
		RDt.y dtRunDate
FROM maxRDt RDt
JOIN maxSDt SDt ON Rdt.x = SDt.x

It should still be optimized but this should do.

Update... what Sean Lange posted is much better and will produce a much simpler query plan. I had not seen his last post when I posted this. Both of our approaches are better than a cursor or loop.

-- AJB
xmlsqlninja.com
Post #1371124
Lokesh Vij
Posted Wednesday, October 10, 2012 10:18 PM


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This query would give the best performance from all the queries posted above 

SELECT dtStartDate,
       (SELECT Max(dtRunDate)
        FROM   #EnrollmentDates
        WHERE  dtRunDate <= #TestDates.dtStartDate)
FROM   #TestDates

I am certainly not trying to compete with experts like Sean here. But just came up with my own better version

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Post #1371201
yogi123
Posted Thursday, October 11, 2012 7:14 AM
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Hi Sean

There is slight difference in requirement

so the table and data as follows 
CREATE TABLE #TestDates
(
	iSchoolYearCode int NOT NULL,
	dtStartDate DATETIME NOT NULL
)


insert into #TestDates values (2011,'2011-08-22 00:00:00.000')
insert into #TestDates values (2011,'2011-12-14 00:00:00.000')
insert into #TestDates values (2011,'2012-05-01 00:00:00.000')
insert into #TestDates values (2012,'2012-08-30 00:00:00.000')

CREATE TABLE #EnrollmentDates
(
	iSchoolYearCode int NOT NULL,
	dtRunDate DATETIME NOT NULL
)

insert into #EnrollmentDates values (2010,'2011-06-16 06:00:06.780')
insert into #EnrollmentDates values (2011,'2011-10-14 11:43:48.840')
insert into #EnrollmentDates values (2011,'2011-11-01 06:00:05.353')
insert into #EnrollmentDates values (2011,'2011-12-03 06:00:06.980')
insert into #EnrollmentDates values (2011,'2012-01-11 06:00:06.947')
insert into #EnrollmentDates values (2011,'2012-01-28 06:00:06.733')
insert into #EnrollmentDates values (2011,'2012-02-11 06:00:07.130')
insert into #EnrollmentDates values (2011,'2012-03-10 06:00:09.083')
insert into #EnrollmentDates values (2011,'2012-04-14 06:00:08.330')
insert into #EnrollmentDates values (2011,'2012-05-12 06:00:11.163')
insert into #EnrollmentDates values (2011,'2012-06-14 06:00:07.893')
insert into #EnrollmentDates values (2012,'2012-10-08 23:47:43.897')


now, if the TestDate is first date of Year, then need to update first enroll date from #EnrollmentDates

so now desired output looks like

dtStartDate			dtRunDate
2011-08-22 00:00:00.000		2011-10-14 11:43:48.840
2011-12-14 00:00:00.000		2011-12-03 06:00:06.980
2012-05-01 00:00:00.000		2012-04-14 06:00:08.330
2012-08-30 00:00:00.000		2012-10-08 23:47:43.897


That means we need to display first Enrollment date for first test date for particular Year.

Please help me one more time to build this.
Post #1371453
Sean Lange
Posted Thursday, October 11, 2012 7:41 AM


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Lokesh Vij (10/10/2012)
This query would give the best performance from all the queries posted above 

SELECT dtStartDate,
       (SELECT Max(dtRunDate)
        FROM   #EnrollmentDates
        WHERE  dtRunDate <= #TestDates.dtStartDate)
FROM   #TestDates

I am certainly not trying to compete with experts like Sean here. But just came up with my own better version


I am certainly no expert and this is by no means a competition. This is definitely a better version than mine. Not sure why I used top instead of max.

_______________________________________________________________

Need help? Help us help you.

Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.

Need to split a string? Try Jeff Moden's splitter.

Cross Tabs and Pivots, Part 1 – Converting Rows to Columns
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs
Post #1371482
Alan.B
Posted Thursday, October 11, 2012 8:19 AM


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Lokesh Vij (10/10/2012)
This query would give the best performance from all the queries posted above 

SELECT dtStartDate,
       (SELECT Max(dtRunDate)
        FROM   #EnrollmentDates
        WHERE  dtRunDate <= #TestDates.dtStartDate)
FROM   #TestDates

I am certainly not trying to compete with experts like Sean here. But just came up with my own better version


I cleaned my original up which runs much faster but can't compete with Lokesh Vij's example above. 
;WITH dt AS
(
	SELECT	DENSE_RANK() OVER (ORDER BY tdt.dtStartDate) x,
			tdt.dtStartDate,
			edt.dtRunDate
	FROM #TestDates tdt
	JOIN #EnrollmentDates edt 
	ON tdt.dtStartDate > edt.dtRunDate
),
maxSDt AS
(
	SELECT DISTINCT x,
			MAX(dtStartDate) OVER (PARTITION BY x) dtStartDate,
			MAX(dtRunDate) OVER (PARTITION BY x) dtRunDate
	FROM dt
)
SELECT	dtStartDate,
		dtRunDate
FROM maxSDt

-- AJB
xmlsqlninja.com
Post #1371528
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