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Introduction to Modern Databases

Join Operations

Explore join operations to combine data from multiple tables using Theta Join, Equi Join, and Natural Join techniques. Understand the Division operator for all-quantifier queries. This lesson helps you express these joins in relational algebra and apply them for practical database querying.

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Imagine our OnlineStore is going very well and we want to see the name of every product along with its supplier’s name. But these two pieces of information live in separate tables: Products and Suppliers. How do we bring this information together? This is where join operations come into play. Join operations are the backbone of relational databases, allowing us to connect data across multiple tables to answer complex questions that a single table alone cannot.

By the end of this lesson, we will be able to:

  • Understand why joining tables is a fundamental concept in relational databases.

  • Differentiate between various types of joins, including the Theta Join, Equi Join, and Natural Join.

  • Grasp the purpose and application of the Division operator for “for all” type queries.

  • Express these operations using formal relational algebra notation.

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The power of combining data with joins

In a well-designed relational database, data is organized into multiple tables to avoid redundancy and improve data integrity. For instance, in our OnlineStore database, we have a ...