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OCA Oracle Database 11g: SQL Fundamentals I: A Real-World Certification Guide by Steve Ries

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Investigating further rules for subqueries

Aside from the basic differences involved with using subqueries, there are a few additional facts we should remember. We take a look at these rules in this section.

Nesting subqueries

A subquery is a query that is nested within another query. However, subqueries can also be nested inside other subqueries. Multiple nested subqueries allow us to use queries from more than two tables, although they can also be used with a single table. An example of this is shown in the following screenshot with indentation and line separation to make the different queries more distinct:

Nesting subqueries

Here, we have three distinct queries—one ...

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