Over clause in SQL Server
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- Опубліковано 29 вер 2024
- over partition by in sql server 2008
sql server over clause partition
partition by clause in sql server 2008
over partition by clause in sql
In this video we will discuss the power and use of Over clause in SQL Server.
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The OVER clause combined with PARTITION BY is used to break up data into partitions.
Syntax : function (...) OVER (PARTITION BY col1, Col2, ...)
The specified function operates for each partition.
For example :
COUNT(Gender) OVER (PARTITION BY Gender) will partition the data by GENDER i.e there will 2 partitions (Male and Female) and then the COUNT() function is applied over each partition.
Any of the following functions can be used. Please note this is not the complete list.
COUNT(), AVG(), SUM(), MIN(), MAX(), ROW_NUMBER(), RANK(), DENSE_RANK() etc.
Example :
SQl Script to create Employees table
Create Table Employees
(
Id int primary key,
Name nvarchar(50),
Gender nvarchar(10),
Salary int
)
Go
Insert Into Employees Values (1, 'Mark', 'Male', 5000)
Insert Into Employees Values (2, 'John', 'Male', 4500)
Insert Into Employees Values (3, 'Pam', 'Female', 5500)
Insert Into Employees Values (4, 'Sara', 'Female', 4000)
Insert Into Employees Values (5, 'Todd', 'Male', 3500)
Insert Into Employees Values (6, 'Mary', 'Female', 5000)
Insert Into Employees Values (7, 'Ben', 'Male', 6500)
Insert Into Employees Values (8, 'Jodi', 'Female', 7000)
Insert Into Employees Values (9, 'Tom', 'Male', 5500)
Insert Into Employees Values (10, 'Ron', 'Male', 5000)
Go
Write a query to retrieve total count of employees by Gender. Also in the result we want Average, Minimum and Maximum salary by Gender.
This can be very easily achieved using a simple GROUP BY query as show below.
SELECT Gender, COUNT(*) AS GenderTotal, AVG(Salary) AS AvgSal,
MIN(Salary) AS MinSal, MAX(Salary) AS MaxSal
FROM Employees
GROUP BY Gender
What if we want non-aggregated values (like employee Name and Salary) in result set along with aggregated values
You cannot include non-aggregated columns in the GROUP BY query.
SELECT Name, Salary, Gender, COUNT(*) AS GenderTotal, AVG(Salary) AS AvgSal,
MIN(Salary) AS MinSal, MAX(Salary) AS MaxSal
FROM Employees
GROUP BY Gender
The above query will result in the following error : Column 'Employees.Name' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause
One way to achieve this is by including the aggregations in a subquery and then JOINING it with the main query as shown in the example below. Look at the amount of T-SQL code we have to write.
SELECT Name, Salary, Employees.Gender, Genders.GenderTotals,
Genders.AvgSal, Genders.MinSal, Genders.MaxSal
FROM Employees
INNER JOIN
(SELECT Gender, COUNT(*) AS GenderTotals,
AVG(Salary) AS AvgSal,
MIN(Salary) AS MinSal, MAX(Salary) AS MaxSal
FROM Employees
GROUP BY Gender) AS Genders
ON Genders.Gender = Employees.Gender
Better way of doing this is by using the OVER clause combined with PARTITION BY
SELECT Name, Salary, Gender,
COUNT(Gender) OVER(PARTITION BY Gender) AS GenderTotals,
AVG(Salary) OVER(PARTITION BY Gender) AS AvgSal,
MIN(Salary) OVER(PARTITION BY Gender) AS MinSal,
MAX(Salary) OVER(PARTITION BY Gender) AS MaxSal
FROM Employees
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Amazing video, thanks a lot!
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OVER Partintion by RULES. And Venkat Rules ! Tahnk U for educating community. I watched all your videos and i'm impressed. Thank U . Yoy are the best teacher in the world and youtube !
This is the only correct way of explaining OVER: by relating it with GROUP BY.
Thank you for this video! Clean, clear, and I really appreciate the comparisons to other methods.
Dear sir it s very nice and i am watching ur videos up to 68 part i learning every day new concepts
Among the best Teachers I have found on UA-cam. He has that skills of shredding complex things and explaining it in a simple manner. Kudos !
You're a great teacher. Thanks
Thank you! It is a very helpfull video tutorial. Now the Over clause is realy clear for me.
Awesome video. So nicely explained!!!!
Thank you sir!!
Thank You
Hi, Could you please also explain how to us Red Gate s/w for transferring data from one server to another
Forgive my ignorance but wouldn't the query in the JOIN clause be a Derived table and not a sub query?
Hello Venkat,
In this example, in over clause, we are not specifying rows between clause. How its summing up all the rows values. Ideally it should take unbounded preceeding and current row as default.
Can you please explain
The default window frame without the ORDER BY is the whole partition. But when you use the ORDER BY, the default window frame is RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW.
why this is no ROWS clause in OVER() but the AVG() calculates for all rows in the partition?
SELECT COUNT(GENDER) AS GENDER_TOTAL,GENDER,NAME,SALARY,AVG(SALARY) AS AVG_SAL,
MIN(SALARY) AS MIN_SAL,
MAX(SALARY) AS MAX_SAL
FROM EMPLOYEES
GROUP BY GENDER; -- thIs works in MYSQL dont know how
The best Teachers and also the best Programmer who have too much clear concept I have found on UA-cam
Hi Venkat. Thank you for your tutorials. Can I ask. I thought the OVER clause had to be used with the ORDER BY clause. I'm just wondering here why the default 'RANGE BY UNBOUNDED PRECEEDING AND UNBOUNDED CURRENT ROW' does not apply here. Is it because you have used the PARTITION BY clause without the ORDER BY clause? Thanks funkychimp
same question....does anyone has it's answer
At 6:22 in over clause used table, how do you get Name column Tom Ron Ben Todd Mark John in this sorting. Can someone xplain please, Thanks in advance
why didn't you use "unbounded preceding and unbounded following" here as u used in other video?.....could u please explain it
The number of views for videos such as these makes me worry for our future. This video should have 2M views by now.... oh wait, let's go watch baby shark one more time
I really understood. Before, I always stucked with this problem: whenever I want to retrieve columns like names, salary etc. as grouping with another column that error comes up. However, if we use subquery we'll able to fix that. But subquery may be fuzzy so that we use over. It's brillant, I'm really happy to understand this.
Thanks for the video and making it easy to understand!
We are partitioning 4 times in this example. Which query would be an optimal one in terms of performance?
On page 6 of the slide, how come Gender is in the subquery when it doesn't have aggregations?
What I love about your videos is that you stick to one topic. You don't add material that is not directly related. It makes my life easier. Thank you.
You have really simplified my work in SQL queries, thank you sir
thank you for sharing this knowledge...it really helped me today. ✌
Venkat, You should have a lot more subscribers.. Your vids are tops!!
This is amazing!!! You are very good at explaining complex concepts and make them easy to understand
Does over function don't take default range as unbounded preceding and current row ??
hi sir .good afternoon
thank you for providing video tutorial of .net
sir would you teach, about data View and its uses and properties
And DataTable
Thank you for taking the time to post this video. Your explanation of this function was the best I have seen when trying to figure out the use of the "Partition.. Over()" function. Very helpful.
easily understandable, great job!
Very well explained, thank you!
Very good explanation, superrrrr !!! thanks 💕
Very Well explained
Alternate Solution using CTE
select Gender,count(Gender) GenderTotal,avg(Salary) AvgSalary, Min(Salary) as MIN , Max(Salary) as MaxSalary from
(select Salary,Gender,Count(Gender) over (partition by Gender) as RN from Employees )
result
group by Gender
Very nice! Another useful tool! Thanks.
This actually the way I would like to teach. You show how complicated a solution is and you show and explain a simpler solution, thanks kudos excilent!
Superb explanation thanks alot
what a powerful tool! -over.
Kudos very well explained sir good example taken. Please bring a SQL interview series. Nowadays it well appreciated by audience.
This is an excellent channel. I am so glad I found it!
Super neat concept! Is there a large performance difference between sub query vs over method?
Such clear explanation, thank you!
This was an amazing and easy to understand explanation of over and partition by in relation to aggregate functions!!! Thank you!!!
This was an excellent example for the OVER and PARTITION BY clauses. I learned a lot by watching this, again, excellent!!!
Thank you very very much!!!🙏🙏
Thanks for the amazing n interesting videos. Helps a lot in our daily tasks.
I am not sure the discussion forum is active. Could you please explain how to extract only the Max. Salaries for Male and Female along with other column fields for that record. Thanks !
You are a great teacher. Very good examples, very helpful tutorials, and your English is really good so it is easy to follow along to your instruction!
How come the avg in the over clause is not generating running average, I am confused what generates a running aggregate or just one value per partition by
very nice...thank u so much...
Awesome Explanation!
To the point this is good stuff👌👍
thank you merlin :-D
great video, thanks!
Thanks @kudvenkat for such clean explanation! I was confused about use of over for long time and I struck the gold here
thankyou very much
this is so amazing stuff
Nicely explained!
thnx u for ur services
Very well explained! New subscriber inserted to the table.
AWESOME ....!
THANK U SIR...!
Thank you 💌
Excellent tutorial video with practical samples, thank you.
thankyou great tut
Well explained 👍
simply awesome
Amazing tutorial. Thank you
Thank you Yen. Means a lot. Your review and feedback really helps. Hope you have a few minutes to write a review. Thank you for your time.
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Indian, Always amazing! What would about us, without them?!
+Yuri Fontoura What would about us, indeed.
+Yuri Fontoura _ at least he is explaining difficult concepts man pardon his english
+malhar jajoo I'm not criticizing him, in any way. Quite opposite of that. I just noticed the Indians are in everywhere seeding great materials. As SQLAuthority and JavaBrains channel have done as well.
Excellent video,clear logic ! thanks a million man
Great!
Genus on the way you explained this !! Thank you !!
👍
thanks
Thank you, the video is so useful!!!
This is very clear, thank you so much!
this mean a lot for me thanks for teaching the world
Thank you so much it was great help
Thank you so much. You are an awesome teacher
Easy and comprehensive
Thanks
Well explained video. Thank you.
You are ray of light for lot of people Venkat. … God bless you !!!!!
Hello Mudasir - Thank you very much Greatly honoured. 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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Great Video, pretty clear and didactic.
Excellent teaching as always!
Great explanation and examples.
Well explained! Thanks
Thanks! This helped!
Thanks you! very useful!
superbly done. Kudos.. :)
Thank you very much!!!
Thank you for these tutorials, they are really great.
Thank you Venkat.. :)
Yu da best!!!
WHAT DO OVER(*) ?
As usual perfect
you get a 10+.
Thanks mate!
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My respect