Window functions in SQL Server
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- Опубликовано: 6 сен 2024
- sql server window function example
window function sql server example
sql server rows range clause
sql server rows between 1 preceding and 1 following
In this video we will discuss window functions in SQL Server
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In SQL Server we have different categories of window functions
Aggregate functions - AVG, SUM, COUNT, MIN, MAX etc..
Ranking functions - RANK, DENSE_RANK, ROW_NUMBER etc..
Analytic functions - LEAD, LAG, FIRST_VALUE, LAST_VALUE etc...
OVER Clause defines the partitioning and ordering of a rows (i.e a window) for the above functions to operate on. Hence these functions are called window functions. The OVER clause accepts the following three arguments to define a window for these functions to operate on.
ORDER BY : Defines the logical order of the rows
PARTITION BY : Divides the query result set into partitions. The window function is applied to each partition separately.
ROWSor RANGE clause : Further limits the rows within the partition by specifying start and end points within the partition.
The default for ROWS or RANGE clause is
RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
Let us understand the use of ROWS or RANGE clause with an example.
Compute average salary and display it against every employee
We might think the following query would do the job.
SELECT Name, Gender, Salary,
AVG(Salary) OVER(ORDER BY Salary) AS Average
FROM Employees
As you can see from the result, the above query does not produce the overall salary average. It produces the average of the current row and the rows preceeding the current row. This is because, the default value of ROWS or RANGE clause (RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) is applied.
To fix this, provide an explicit value for ROWS or RANGE clause as shown below. ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING tells the window function to operate on the set of rows starting from the first row in the partition to the last row in the partition.
SELECT Name, Gender, Salary,
AVG(Salary) OVER(ORDER BY Salary ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS Average
FROM Employees
The same result can also be achieved by using RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
Well, what is the difference between ROWS and RANGE
We will discuss this in a later video
The following query can be used if you want to compute the average salary of
1. The current row
2. One row PRECEDING the current row and
3. One row FOLLOWING the current row
SELECT Name, Gender, Salary,
AVG(Salary) OVER(ORDER BY Salary ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING) AS Average
FROM Employees
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It's been 7 years and still, this tutorial series is far better than every other material on SQL :)
Hands Down, Thanks a lot!
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@@RohitKumar-qo7pt Because of the clarity in his presentation, the lucid way of explaining such concepts. He deserves to get a medal.
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Hello Venkat gaaru, great work . Just to add on for the default value of ROWS or RANGE values in OVER() Clause, which varies based on ORDER BY clause
--The default value of ROWS or RANGE clause is "RANGE BETWEEN UNBOUNDED PRECEEDING AND CURRENT ROW" If the ORDER BY clause is specified
--The default value of ROWS or RANGE clause is "ROWS BETWEEN UNBOUNDED PRECEEDING AND UNBOUNDED FOLLOWING" If the ORDER BY clause is not specified i.e the entire window.
Please correct me, if anything is wrong. Kudos to your work and Thank you🙏.
Best tutorial available on the net . Thank you for your hard job . You are the best teacher on the planet. The way of teaching is just superb! Greetings from Poland !
After 20 years as software developer, it's the fist time that I pay attention to the adventage of window function, I'v been using the subqueries to get this kind of results, but with a very low performance in execution time.
Great video! Thanks a lot!
One thing I would add is that instead of writing BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING statement, we could remove the ORDER BY entirely and just write:
AVG(SALARY) OVER() as Average
This is gold! I have been struggling to understand Window functions and syntax and your explanation makes it all clear now.
if you use just this: AVG(Salary) OVER() - then whole set is used for computing average. But as soon you put order by into OVER, default value for ROWS and RANGE are taken into calculation. I would expect that just using ORDER BY should not affect calculation of AVG, but it does - it completely changes result set on which calculation is made.
would test , thanks for letting us know
Yes, AVG(Salary) OVER () seems to have the same result
Nice tip
Amazing explanation. Thank you!
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Keep up the great work. I hope you do more topics.
You're a natural born teacher. You're doing what you were born to do. Keep up the good work!
This is the best tutorial on windows functions on youtube. Thank you so much for this.
What an amazing teacher! Thank you so much for breaking down these concepts for us! :)
Hello Justin - Thank you very much for the feedback. Means a lot. I have included all the sql tutorial videos, slides and text articles in sequence on the following page. Hope you will find it handy.
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I was struggling to understand windows functions and you have explained it with so ease .Its just awesome.Please keep posting such videos.Thanks a lot :)
very very good and clear teaching.
Can't believe this doesn't have more views!
Freely available at this quality is incredible...god bless!
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Good attention to detail
Thanks a lot
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Great sir This video helps me lot thank u so much 🙏🙏
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Thank you Venkat!
really a very detailed explanation.
Hats off bro...easy to follow and well explained!
One of the best explanation of the concept of Windows function! I have referenced to lots of tutorials online, but this one really stands out to me :) Kudos gentleman!
The best video on Window functions so far! highly recommend!!
Words cannot translate the emotions . Only can say excellent presentation in clearing the concepts. Thank you from core of heart.
you explained it so well, thankyooou
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This is a really comprehensive tutorial! Thank you so much!
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Worth watching
Thanks! very helpful content
Best video for understanding window functions.
Awesome explanation
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Great explanation 👍🏽
Thanks great video 👍🏽
GREAT JOB!!!
Wow. Thanks brother ❤
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keep it up! extremely well made tutorial! :)
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video was straight forward and detailed, thank you for sharing your knowledge
Simplicity of your explanation is remarkable. Keep it up.
super helpful
Very helpful video, clearly and nicely explained . Thanks !
Thank you Venkat Sir.
very well explained with simplicity. Great Work.
Sir u r great
very neat and to the point explanation !
What an explanation! Thank you!
Thank you so much! Best tutorial!
you made it so clear and precise...thank you
Very detailed video.... Thank you :)
Thanks for the video. It was really helpful
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Great Video. Thank you for posting.
Very informative
Great video! Thank you, it is much clearer now!
Great video, Many thanks
To the point, very nice explanations . Thank you :)
Thank you so much and appreciate your work.
Very good explanation
Hi Venkat, first off I enjoy your videos a lot, very helpful for interviews.
I have a question related to analytic window function (sum)
Could you please confirm which version of MS SQL Server are you using? Not 2008 right?
Because, I tried running below query in 2008 version which is quite similar to what you demonstrated in of your slides in above video and it threw syntax error.
select *, sum(sales) over(order by sales) as sumofsales from test1......error
select *, sum(sales) over() as sumofsales from test1.......no error it ran successfully
select *, sum(sales) over(partition by dealer) as sumofsales from test1.......no error it ran successfully
The reason why the first query failed makes sense to me, because I believe there is no need at all for a order by argument in analytic window function; partition by argument might be required sometimes though (my 3rd query)
I got confused because your query (quite similar to mine, as per above logic it should have failed since it contained order by arguement in analytical window function you demonstrated) ran successfully...
Seems like you are using a different SQL version than mine...Just curious to know why your query did not fail :)
Thanks again for comprehensive, well articulated and ofcourse free videos :)
Regards,
Romil
Thank you. That was extremely clear
Good tutorial. Partition by Gender order by Salary. Why salary is not in ascending order?
Thanks man, apreciate your work you've done here :) helpfull, keep doing good work :)
Too good, thank you so much
venkat sir could u explain realtime queries in fucntions
Отличное видео
Excellent!!!
great..
Is there anyway to set the preceeding/following row clause programatically so that i can write one function that can output moving average of variable window width? (without using dynamic queries)
Thanks
Running average by accident, I love it!
You are my Guru 🙏
Why can't we directly use partition by instead of specifying Unbounded values? In video 108 this is achieved by Partitioning it right?
Thanks sir!!
i think we have to use ID column for Order By Clause to avoid duplicates.....
thanks so much
Ngubk
Your voice sounds like Sadhguru
If we just use OVER() without specifying anything inside over then it is an equivalent to mentioning UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING.
SQL Knowledge Hub on Internet _/\_
For >> PARTITION BY GENDER ORDER BY SALARY >>>>>> order of salary is correct for FEMALE but why order is incorrect for MALE resultset