هل nested select سيئة ؟ ولماذا؟

تم تعديل 25 أكتوبر 200619 سنة بواسطة ammartalal2005

مرحبا

Correlated sub-query or nested query is bad, because for every record in the outer query, then inner query will have to execute.

You cannot say it is bad in general, if you need it,and you have no alternative, ,then it is OK,

If you want me to answer you correctly, then you have to answer me first, Is the join operation bad?
The actual answer is that it depends on the data and the usage and most importantly, the no of blocks that needs to be executed to retrieve the .result

You can find an interesting paper about tuning and how to measure tuning on my website

www.e-ammar.com/download.htm

then download the document called

Tuning your application using SQL optimization Techniques PDF 41KB

it will teach you the basics of tuning

regards

Ammar Sajdi
oracle consultant
amman - Jordan
www.e-ammar.com
PALCO/REALSOFT

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