Query Help
-
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 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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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?
-
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/ -
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
-
yogi123 (10/10/2012)
Hello EveryoneI 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
-
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 questionsLink to my Blog Post --> www.SQLPathy.com[/url]
Follow me @Twitter
-
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.
-
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/ -
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
-
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
-
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
-
select dtStartDate,dtRunDate from #TestDates
cross apply (select top 1 * from #EnrollmentDates
where dtRunDate<=#TestDates.dtStartDate order by dtRunDate desc ) b
-
cooljagadeesh (10/11/2012)
select dtStartDate,dtRunDate from #TestDatescross 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/
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