Joins

Joins are operations in database management systems that combine records from two or more tables based on a related column between them. They are used to retrieve data that is spread across multiple tables.

Joins are essential for querying relational databases where data is normalized into separate tables. By using joins, you can retrieve a comprehensive set of data that combines information from multiple tables, linked by a common attribute. There are different types of joins, including inner join, left join, right join, and full outer join, each serving a specific purpose.

Example:

Here’s an example of using joins in SQL:

Suppose we have two tables, Orders and Customers:

Orders table:

Customers table:

To retrieve a list of orders along with the customer names, you can use an inner join:

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

This will produce the following result:

In this example:

• The INNER JOIN clause combines rows from the Orders and Customers tables where there is a match in the CustomerID column.
• The resulting table includes only the orders with matching customer records, showing the OrderID, CustomerName, and OrderDate.