Oracle INNER JOIN

Introduction

In Oracle, INNER JOIN is a type of join that combines rows from two or more tables based on a related column between them. It returns only the matched rows that satisfy the join condition.

Syntax

The syntax for an INNER JOIN in Oracle is as follows:

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

In this syntax:

• table1 and table2 are the tables you want to join.
• column_name is the column that is common between the tables used to join them.
• column1, column2, ... are the columns you want to select from the result.

Example

Consider two tables, employees and departments, with a common column department_id.

employees table

| employee_id | employee_name | department_id | |-------------|---------------|---------------| | 1 | John Doe | 1 | | 2 | Jane Smith | 2 | | 3 | Alice Johnson | 1 |

departments table

| department_id | department_name | |---------------|-----------------| | 1 | Sales | | 2 | Marketing | | 3 | Finance |

To join these two tables using INNER JOIN and retrieve employee names along with their department names:

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

The result would be:

| employee_name | department_name | |----------------|-----------------| | John Doe | Sales | | Jane Smith | Marketing | | Alice Johnson | Sales |

Conclusion

INNER JOIN is a useful feature in Oracle that allows you to combine rows from multiple tables based on a common column. It helps in retrieving related data efficiently and obtaining meaningful results.