Correlated subquery in sql Part 60

In this video we will discuss about Corelated Subqueries

In Part 59, we discussed about 2 examples that uses subqueries. Please watch Part 59, before proceeding with this video. We will be using the same tables and queries from Part 59.

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In the example below, sub query is executed first and only once. The sub query resutls are then used by the outer query. In a non-corelated subquery, the subquery can be executed independently of the outer query.
Select [Id], [Name], [Description]
from tblProducts
where Id not in (Select Distinct ProductId from tblProductSales)

If the subquery depends on the outer query for its values, then that sub query is called as a correlated subquery. In the where clause of the subquery below, "ProductId" column get it's value from tblProducts table that is present in the outer query. So, here the subquery is dependent on the outer query for it's value, hence this subquery is a correlated subquery. Correlated subqueries get executed, once for every row that is selected by the outer query. corelated subquery, cannot be executed independently of the outer query.
Select [Name],
(Select SUM(QuantitySold) from tblProductSales where ProductId = tblProducts.Id) as TotalQuantity
from tblProducts
order by Name

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[rezaulhoque]

U hv been serving the community for so many years. Thanks a lot

[aqasuncion]

Thank you for all your videos! I understand that different heads have their own best way of understand things, but your explanations and samples is the one that suits mine!

[Csharp-video-tutorialsBlogspot]

Hi Ravi, you are very welcome. Thank you for asking this question. We will discuss about the performance aspect between subqueries and joins in the next video. Please stay tuned.

[krismaly]

Revisiting.

Thanks for educating the community

Thanks a lot

[Csharp-video-tutorialsBlogspot]

Hi Varadharaj, sorry I don't have any videos on regular expressions yet. I will record and upload videos on regular expression and interview questions on sql server as soon as I can.

[anuragvashishtha]

A precise and easy to understand tutorial. Liked it!

[celina]

Awesome video! Really cleared up the difference between correlated and non correlated subqueries. Thank you!

[adamstearns]

fantastic. thank you for this excellent resource.

[mysqlshorttutorials]

Great, easy to understand. Well done.

[non-dualist]

Awesome!! Coaching institutes never teach us such things.

[krzysztofs]

Very good explanation. Very good examples. Thank U Venkat!

[shohailaamil]

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[kasthuri]

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[rammohan]

Thank u very much venkat,
and  please give me deep information about ' Subqueries'.

[dcgadagprasannakumar]

Best out of all available in youtube,

[YuckNasty]

Thank you! This was incomprehensible when I was reading it.

[AVD]

hi venkat Thank you for sharing your knowledge

[krismaly]

I enjoyed watching this video. Your explanation of basics is very interesting and makes clear understanding of topic. Thanks a lot and good luck!

[ishamadaan]

Venkat you are god :) Thanks for all the amazing videos :)

[Csharp-video-tutorialsBlogspot]

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