Inner Join

The INNER JOIN keyword presents records that have matching values in both tables.

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

Key Points to Remember

• Returns only matching records from both tables.

• Excludes rows that do not have a match.

• Used to retrieve related data from multiple tables.

• Requires a common column for joining.

• Naming the columns - It is a good practice to name the columns in SQL statement to make it look cleaner and easier to understand.

Syntax for joining three tables is as below:

The below example joins departments by matching employees to their departments using employee_id. The joins salaries by matching employees to their salaries using employee_id. The SELECT statement retrieves employee details, department names, and salaries.

SELECT 
    table1.column1, 
    table2.column2, 
    table3.column3
FROM table1
JOIN table2 ON table1.common_column = table2.common_column
JOIN table3 ON table2.common_column = table3.common_column;

Example from the database:
SELECT 
    e.employee_id, 
    e.name, 
    d.department_name, 
    s.salary
FROM employees e
JOIN departments d ON e.employee_id = d.employee_id
JOIN salaries s ON e.employee_id = s.employee_id;

Employee, Department & Salary Data

employee_id	name	department_id	department_name	salary
1	Alice	101	HR	50000
2	Bob	102	IT	60000
3	Charlie	103	Finance	55000
4	David			70000