Topic: SQL*Plus and PL/SQL >> correlated subquery clarification
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| Title: correlated subquery clarification |
| muzu |
Posted: Aug 28, 2007 11:07:08 AM |
Total Post: 37
Joined: Aug, 2007
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Can anyone explain me when we use correlated subqueries rather than nested subqueries.
Do all the correlated subqueries can be written in nested subqueries form as well ?
What are the major conditions that apply whenever we write a correlated subquery(regarding the performance of a query) and why we go for it ?
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 Priya |
| Posted: Aug 29, 2007 08:29:03 AM |  |
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Total Post: 19
Joined: Jul, 2007
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A correlated subquery is a subquery that uses the values from the outer query. We will use it when we need to check some condition which takes the value from the outer query.
For eg;
select book_key, store_key, quantity from sales s
where quantity < (select max(quantity)from sales
where book_key = s.book_key);
Hope this example will help you to understand correlated subquery.
Regards,
Priya
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