Difference Between INNER JOIN and OUTER JOIN in SQL Server

INNER JOIN and OUTER JOIN are two types of joins used in SQL Server to combine data from two or more tables based on a related column between them. The main difference between INNER JOIN and OUTER JOIN is how they handle unmatched rows between the tables being joined.

INNER JOIN:

INNER JOIN retrieves only the matching rows between the tables being joined. If there are no matching rows found, those rows are not included in the result set. It returns rows that have matching values in both tables' columns being joined.

Example:

SELECT * 
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;

OUTER JOIN:

OUTER JOIN retrieves all the rows from at least one of the tables being joined, regardless of whether there is a matching row in the other table. There are three types of OUTER JOINS: LEFT JOIN, RIGHT JOIN, and FULL JOIN.

Example of LEFT JOIN:

SELECT * 
FROM table1
LEFT JOIN table2 ON table1.column_name = table2.column_name;

Example of RIGHT JOIN:

SELECT * 
FROM table1
RIGHT JOIN table2 ON table1.column_name = table2.column_name;

Example of FULL JOIN:

SELECT * 
FROM table1
FULL JOIN table2 ON table1.column_name = table2.column_name;

When to Use Each Type of Join:

• Use INNER JOIN when you only want to retrieve rows that have matching values in the joined columns.
• Use OUTER JOIN when you want to retrieve all rows from one or both tables, including unmatched rows.

Understanding the differences between INNER JOIN and OUTER JOIN is essential for efficiently querying data from multiple tables in SQL Server.