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MySQL - find duplicated values

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In this article, we would like to show you how to find duplicated values in MySQL.

Quick solution:

SELECT `column_name`, COUNT(`column_name`)
FROM `table_name`
GROUP BY `column_name`
HAVING COUNT(`column_name`) > 1;

Practical example

To show how to find duplicated values, we will use the following table:

MySQL - example data used to find duplicated values
MySQL - example data used to find duplicated values

Note:

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

Example

In this example, we will display the number of names that are duplicated in users table.

Query:

SELECT `name`, COUNT(`name`) AS 'name_number'
FROM `users`
GROUP BY `name`
HAVING COUNT(`name`) > 1;

Result:

MySQL - find and count duplicated values
MySQL - find and count duplicated values

Database preparation

create_tables.sql file:

CREATE TABLE `users` (
	`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
	`name` VARCHAR(100) NOT NULL,
	`email` VARCHAR(100) NOT NULL,
	`country` VARCHAR(15) NOT NULL,
	PRIMARY KEY (`id`)
)
ENGINE=InnoDB;

insert_data.sql file:

INSERT INTO `users`
	(`name`, `email`, `country`)
VALUES
	('Tom', 'tom1@email.com', 'Poland'),
	('Tom', 'tom2@email.com', 'Poland'),
    ('Tom', 'tom3@email.com', 'Poland'),
    ('Kim', 'kim1@email.com', 'Vietnam'),
    ('Kim', 'kim2@email.com', 'Vietnam'),
    ('Chris', 'chris1@email.com', 'Spain'),
	('Chris', 'chris2@email.com', 'Spain'),
	('Chris', 'chris3@email.com', 'USA');

MySQL - Problems

MySQL - find duplicated values
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