MySQL EquiJoin

The MySQL EquiJoin is a type of join operation that combines rows from two or more tables based on the equality of values in specified columns. It’s one of the most common types of join operations and is used to establish relationships between tables by matching values in those columns. An equijoin uses the = operator to compare values in the specified columns.

Here’s the basic syntax for performing an equijoin using the JOIN clause in MySQL:

SELECT columns
FROM table1
JOIN table2 ON table1.column_name = table2.column_name;

Let’s break down the components of this syntax:

• SELECT columns: Specifies the columns you want to retrieve from the joined tables. You can select specific columns from both tables.
• FROM table1: Indicates the first table you want to include in the join.
• JOIN table2: Specifies the second table you want to join with the first table.
• ON table1.column_name = table2.column_name: This is the equijoin condition. It defines which columns in each table are used to match rows from the two tables. Rows are combined where the values in these columns are equal.

Here’s a practical example of an equijoin. Let’s say you have two tables, employees and departments, and you want to retrieve the names of employees and their corresponding department names based on a shared department_id:

SELECT employees.employee_name, departments.department_name
FROM employees
JOIN departments ON employees.department_id = departments.department_id;

In this example, the JOIN condition is employees.department_id = departments.department_id, which means that rows are combined where the department_id values match in both tables. This produces a result set that includes the names of employees and their corresponding department names.

Equijoins are fundamental for working with relational databases as they allow you to establish relationships between tables and retrieve data from related tables based on shared values. They are used in many real-world scenarios for querying and reporting purposes.