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MySQL - Left Join

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Created by:

Marcino

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In this article, we would like to show you how to use LEFT JOIN in MySQL.

Quick solution:

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SELECT `column1`, `column2`, `columnN`
FROM `table1`
LEFT JOIN `table2`
ON `table1`.`column_name` = `table2`.`column_name`;

Practical example

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To show how the LEFT JOIN works, we will use the following tables:

Note:

At the end of this article you can find databases preparation SQL queries.

Example

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In this example, we will select all users with department information.

Query:

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SELECT * FROM `users`
LEFT JOIN `departments` 
ON `departments`.`id` = `users`.`department_id`;

Output:

Database preparation

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create_tables.sql file:

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CREATE TABLE `departments` (
    `id` INT(10) UNSIGNED NOT NULL,
    `department_name` VARCHAR(50) NOT NULL,
    `location` VARCHAR(50) NULL,
    PRIMARY KEY (`id`)
);
​
CREATE TABLE `users` (
    `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
    `name` VARCHAR(50) NOT NULL,
    `surname` VARCHAR(50) NOT NULL,
    `department_id` INT(10) UNSIGNED,
    PRIMARY KEY (`id`),
    FOREIGN KEY (`department_id`) REFERENCES `departments` (`id`)
)

insert_data.sql file:

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INSERT INTO `departments`
    (`id`, `department_name`, `location`)
VALUES
    (1, 'Sales', 'New York'),
    (2, 'Finance', NULL),
    (3, 'HR', 'Atlanta'),
    (4, 'Purchase', 'New Orlean'),
    (5, 'Operations', 'Boston');
​
INSERT INTO `users`
    ( `name`, `surname`, `department_id`)
VALUES
    ('John', 'Stewart', 1),
    ('Chris', 'Brown', 2),
    ('Kate', 'Lewis', 3),
    ('Ailisa', 'Gomez', NULL),
    ('Gwendolyn', 'James', 2),
    ('Simon', 'Collins', 4),
    ('Taylor', 'Martin', 2),
    ('Andrew', 'Thompson', NULL);