INNER JOIN: This is the most common type of join. It returns only the rows where there is a match in both tables based on the specified condition. In other words, it returns the intersection of the two tables. For example, if you want to retrieve a list of employees and their respective departments, you would use an INNER JOIN to combine the employee and department tables based on the department id.
LEFT JOIN (or LEFT OUTER JOIN): This type of join returns all the rows from the left table and the matching rows from the right table. If no match is found, NULL values are returned for the right table's columns. This is useful when you want to retrieve all records from one table, even if there's no corresponding data in the other table. For instance, if you want to display a list of all employees, including those not assigned to a department, you would use a LEFT JOIN.
RIGHT JOIN (or RIGHT OUTER JOIN): This join is similar to the LEFT JOIN but works in the opposite direction. It returns all the rows from the right table and the matching rows from the left table. If no match is found, NULL values are returned for the left table's columns. This can be helpful when you want to retrieve all records from the right table, even if there's no corresponding data in the left table.
Remember, choosing the correct type of join is essential for retrieving accurate data and ensuring optimal query performance.