Difference between Inner Join and Outer Join in SQL

JOINS in SQL are fundamental operations used to combine data from multiple tables based on related columns. They are essential for querying data that is distributed across different tables, allowing you to retrieve and present it as a single or similar result set.

In this article, We will learn about Inner Join vs Outer Join in SQL in detail.

What is a JOIN in SQL?

• In SQL, a JOIN is a crucial operation that enables you to combine rows from two or more tables based on a common column.
  
• JOINS are used to consolidate data from multiple tables into a single result set, with various types of JOINS serving specific purposes to achieve different combinations of data.

How to Use an INNER JOIN in SQL

An INNER JOIN returns only the rows where there are matching values in both tables. Rows that do not have a match in the other table are excluded from the result set.

Syntax:

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

Example:

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

This query returns the names of employees along with their corresponding department names where the department_id matches in both tables.

How to Use an OUTER JOIN in SQL

An OUTER JOIN is used to return all the rows from one table and the matching rows from the other table. If there is no match, NULL values are returned for columns from the table without a match.

There are three types of OUTER JOINS: LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN.

1. LEFT OUTER JOIN in SQL

A LEFT OUTER JOIN returns all the rows from the left table and the matching rows from the right table. If there is no match, NULL values are returned for columns from the right table.

Syntax:

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

Example:

SELECT employees.name, departments.department_name
FROM employees
LEFT OUTER JOIN departments
ON employees.department_id = departments.department_id;

This query returns all employees, including those who may not belong to any department (with NULL for department_name).

2. RIGHT OUTER JOIN in SQL

A RIGHT OUTER JOIN returns all the rows from the right table and the matching rows from the left table. If there is no match, NULL values are returned for columns from the left table.

Syntax:

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

Example:

SELECT employees.name, departments.department_name
FROM employees
RIGHT OUTER JOIN departments
ON employees.department_id = departments.department_id;

This query returns all departments, including those without employees (with NULL for name).

3. FULL OUTER JOIN in SQL

A FULL OUTER JOIN returns all rows when there is a match in either left or right table. If there is no match, NULL values are returned for columns from the table without a match.

Syntax:

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

Example:

SELECT employees.name, departments.department_name
FROM employees
FULL OUTER JOIN departments
ON employees.department_id = departments.department_id;

This query returns all employees and all departments, including those that do not have a match in the other table.

INNER JOIN Vs OUTER JOIN in SQL

Difference Between INNER JOIN and OUTER JOIN in Terms of Performance and Reliability

Conclusion

JOINS in SQL are essential for combining data from multiple tables. INNER JOINS are best used when you only need matching rows, while OUTER JOINS (LEFT, RIGHT, FULL) are used when you need to retain unmatched rows from one or both tables. Understanding the differences in performance and reliability between these JOIN types helps in choosing the right one for your query needs.