Joining Tables
Joins are a fundamental aspect of relational databases. They allow you to extract data on entities related by design—represented by related tables—in your database.
A join occurs when you retrieve data from tables related by some shared data, often (but not necessarily) a shared reference number or index. For example, if you have a table of customers and a table of orders, good design in a relational database will ensure that the two are related together by some common data between the tables, perhaps by storing a customer number on every order record. By performing a join, you can retrieve information in a resultset where each row combines data from both tables: information about each order will be combined with information about ...
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