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Query Help

yogi123

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Points: 2932
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October 10, 2012 at 1:20 pm

#268409

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
dtStartDatedtRunDate
2011-08-22 00:00:00.0002011-06-16 06:00:06.780
2011-12-14 00:00:00.0002011-12-03 06:00:06.980
2012-05-01 00:00:00.0002012-04-14 06:00:08.330
2012-08-30 00:00:00.0002012-06-14 06:00:07.893
Please help me to build the logic for this
Thanks

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Sean Lange SSC Guru Points: 286590 More actions · Answer 1

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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Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/

yogi123 SSCrazy Points: 2932 More actions · Answer 2

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?

Sean Lange SSC Guru Points: 286590 More actions · Answer 3

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 Modens splitter http://www.sqlservercentral.com/articles/Tally+Table/72993/.

Cross Tabs and Pivots, Part 1 – Converting Rows to Columns - http://www.sqlservercentral.com/articles/T-SQL/63681/
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/

yogi123 SSCrazy Points: 2932 More actions · Answer 4

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

Alan Burstein SSC Guru Points: 61141 More actions · Answer 5

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
dtStartDatedtRunDate
2011-08-22 00:00:00.0002011-06-16 06:00:06.780
2011-12-14 00:00:00.0002011-12-03 06:00:06.980
2012-05-01 00:00:00.0002012-04-14 06:00:08.330
2012-08-30 00:00:00.0002012-06-14 06:00:07.893
Please help me to build the logic for this
Thanks

This is what I came up with...

WITH dt AS

(

SELECTDENSE_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

)

SELECTSDt.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.

"I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code."

-- Itzik Ben-Gan 2001

Lokesh Vij SSChampion Points: 10836 More actions · Answer 6

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 😀

~ Lokesh Vij

Guidelines for quicker answers on T-SQL question[/url]
Guidelines for answers on Performance questions

Link to my Blog Post --> www.SQLPathy.com[/url]

Follow me @Twitter

yogi123 SSCrazy Points: 2932 More actions · Answer 7

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

dtStartDatedtRunDate

2011-08-22 00:00:00.0002011-10-14 11:43:48.840

2011-12-14 00:00:00.0002011-12-03 06:00:06.980

2012-05-01 00:00:00.0002012-04-14 06:00:08.330

2012-08-30 00:00:00.0002012-10-08 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.

Sean Lange SSC Guru Points: 286590 More actions · Answer 8

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 Modens splitter http://www.sqlservercentral.com/articles/Tally+Table/72993/.

Cross Tabs and Pivots, Part 1 – Converting Rows to Columns - http://www.sqlservercentral.com/articles/T-SQL/63681/
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/

Alan Burstein SSC Guru Points: 61141 More actions · Answer 9

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

(

SELECTDENSE_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

)

SELECTdtStartDate,

dtRunDate

FROM maxSDt

"I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code."

-- Itzik Ben-Gan 2001

Eugene Elutin SSC Guru Points: 59322 More actions · Answer 10

That may win a bit:

SELECT td.dtStartDate

,Max(dtRunDate)

FROM #TestDates td

LEFT JOIN #EnrollmentDates ed

ON ed.dtRunDate <= td.dtStartDate

group by td.dtStartDate

_____________________________________________
"The only true wisdom is in knowing you know nothing"
"O skol'ko nam otkrytiy chudnyh prevnosit microsofta duh!":-D
(So many miracle inventions provided by MS to us...)

How to post your question to get the best and quick help[/url]

Eugene Elutin SSC Guru Points: 59322 More actions · Answer 11

I'm a bit confused with OP last requirements. Looks like expected outcome doesn't corresponds to:

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

May be something like that:

;with CTE1

AS

(

SELECT td.dtStartDate

,MAX(ed.dtRunDate) dtRunDate

,YEAR(td.dtStartDate) sdYear

FROM #TestDates td

LEFT JOIN #EnrollmentDates ed

ON ed.dtRunDate <= td.dtStartDate

group by td.dtStartDate

)

, CTE2

AS

(

SELECT sdYear, MIN(dtRunDate) dtRunDate

FROM CTE1

GROUP BY sdYear

)

SELECT c1.dtStartDate, c2.dtRunDate

FROM CTE1 c1

JOIN CTE2 c2

ON c2.sdYear = c1.sdYear

_____________________________________________
"The only true wisdom is in knowing you know nothing"
"O skol'ko nam otkrytiy chudnyh prevnosit microsofta duh!":-D
(So many miracle inventions provided by MS to us...)

How to post your question to get the best and quick help[/url]

cooljagadeesh SSC Eights! Points: 959 More actions · Answer 12

select dtStartDate,dtRunDate from #TestDates

cross apply (select top 1 * from #EnrollmentDates

where dtRunDate<=#TestDates.dtStartDate order by dtRunDate desc ) b

Sean Lange SSC Guru Points: 286590 More actions · Answer 13

cooljagadeesh (10/11/2012)
select dtStartDate,dtRunDate from #TestDates
cross apply (select top 1 * from #EnrollmentDates
where dtRunDate<=#TestDates.dtStartDate order by dtRunDate desc ) b

This looks strikingly similar to the one I posted yesterday. The version using MAX that Lokesh posted will beat this on performance.

_______________________________________________________________

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 Modens splitter http://www.sqlservercentral.com/articles/Tally+Table/72993/.

Cross Tabs and Pivots, Part 1 – Converting Rows to Columns - http://www.sqlservercentral.com/articles/T-SQL/63681/
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/