Left Join vs Right Join - (MySQL Join)

When working with databases, it is often necessary to join multiple tables to retrieve the required data. In this tutorial, we'll discuss left join and right join in MySQL, which are commonly used types of joins.

Syntax

The syntax for left join in MySQL is as follows:

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

The syntax for right join in MySQL is as follows:

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

Example

Let's say we have two tables: "orders" and "customers". The "orders" table has a "customer_id" column that references the "id" column in the "customers" table. We want to retrieve all orders with the corresponding customer name. Here's how we can implement left join:

SELECT orders.id, customers.name
FROM orders
LEFT JOIN customers
ON orders.customer_id = customers.id;

Similarly, here's how we can implement right join:

SELECT orders.id, customers.name
FROM orders
RIGHT JOIN customers
ON orders.customer_id = customers.id;

Output

The output of the left join example will be a table with two columns: "id" and "name". The "id" column will contain order IDs, and the "name" column will contain customer names. If there is no corresponding customer name for an order, the "name" column will be NULL.

The output of the right join example will be similar to the left join example, but with the addition of all the customers that don't have orders. If there is no corresponding order for a customer, the "id" column will be NULL.

Explanation

In the left join example, we used the left join operator to join the "orders" table with the "customers" table on the "customer_id" and "id" columns, respectively. This allowed us to retrieve all orders with the corresponding customer names, even if there were no orders for some customers.

Similarly, in the right join example, we used the right join operator to retrieve all customers with the corresponding order IDs, even if there were no customers for some orders.

Use

Left join and right join are commonly used types of joins in MySQL. Left join is used to retrieve all records from the left table and only matching records from the right table. Right join is used to retrieve all records from the right table and only matching records from the left table. These types of joins are useful when you want to include all records from one table, even if there are no matching records in the other table.

Important Points

• In a left join, all records from the left table are returned, and matching records from the right table are included.
• In a right join, all records from the right table are returned, and matching records from the left table are included.
• If there are no matching records in the right table for a left join, the corresponding columns in the result set will be NULL.
• If there are no matching records in the left table for a right join, the corresponding columns in the result set will be NULL.

Summary

In this tutorial, we discussed left join and right join in MySQL, which are commonly used types of joins. We covered the syntax, example, output, explanation, use, and important points of these joins in MySQL. With this knowledge, you can now use left join and right join to join multiple tables in MySQL and retrieve the required data.