Using JOINs to Combine Data from Multiple Tables

In SQL, JOIN operations are used to combine data from multiple tables based on related columns. When we use JOIN, we actually use INNER JOIN, the most common type of join which returns only the rows that have matching values in both tables being joined.

JOIN Syntax

To JOIN two tables in order to combine their data, we use the following syntax:

SELECT column1, column2, ...
FROM table1
INNER JOIN table2 ON table1.column = table2.column;

table1, table2: Specifies the tables to be joined.
column: Represents the related columns between the tables.

Consider two tables, “employees” and “departments,” with a common column “department_id” in both tables. To retrieve a list of employees along with their corresponding department names, you can use a JOIN:

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

The above query combines data from the “employees” and “departments” tables based on the matching “department_id” values. The result set includes the employee ID, employee name, and department name.

By using JOINs, you can leverage the relationships between tables to combine data and retrieve meaningful insights. The JOIN (or INNER JOIN) specifically allows you to retrieve rows that have matching values in both tables, ensuring that only relevant data is included in the result set. We will also explore other types or JOINs.