CROSS JOIN in MySQL Workbench

• Let's explore CROSS JOINs in MySQL using an example.

• A CROSS JOIN, also known as a Cartesian Join, produces the Cartesian product of two or more tables. It combines every row from the first table with every row from the second table (and subsequent tables) to create a result set with all possible combinations. CROSS JOINs are typically used when you need to generate all possible combinations, but they can result in a large number of rows, so they should be used with caution.

• Let's use a simple example with two hypothetical tables: `colors` and `sizes`. The `colors` table contains different colors, and the `sizes` table contains different sizes.

• colors table:

    -- Create the 'colors' table

    CREATE TABLE colors (

        color VARCHAR(20) PRIMARY KEY

    );

    -- Insert data into the 'colors' table

    INSERT INTO colors (color)

    VALUES

        ('Red'),

        ('Green'),

        ('Blue');

• sizes table:

    -- Create the 'sizes' table

    CREATE TABLE sizes (

        size VARCHAR(20) PRIMARY KEY

    );

    -- Insert data into the 'sizes' table

    INSERT INTO sizes (size)

    VALUES

        ('Small'),

        ('Medium'),

        ('Large');

• If you perform a CROSS JOIN between these two tables, you'll get all possible color and size combinations:

    SELECT colors.color, sizes.size

    FROM colors

    CROSS JOIN sizes;

• The result of this query would be:

• As you can see, the query generates every combination of colors and sizes. Each color is combined with each size, resulting in a total of 9 rows.

• CROSS JOINs are not commonly used for practical scenarios where you want to retrieve meaningful data. They are more commonly used for generating all possible combinations in specific cases, such as creating test data or when you explicitly need every combination for a specific analysis. Keep in mind that the result of a CROSS JOIN can quickly become large and unwieldy, so it's important to use them judiciously.