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SQL Basics
Joins

Constraints



Oracle SQL Joins


In a SELECT statement, a join combines data from two or more tables to produce the required results.

So far, all of our SQL has been centered around a single table called COUNTRY. In reality, of course, a database will consist of many more tables like this:

Schema diagram for world model

We could certainly enquire on each table individually, but we discover the real power of the relational database when we start to merge data from several tables to produce the results. SQL joins allow us to do just that.
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