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PostgreSQL - find duplicated values

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Created by:
leila
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In this article, we would like to show you how to find duplicated values in PostgreSQL.

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:

PostgreSQL - example data used to find duplicated values
PostgreSQL - 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:

PostgreSQL - find and count duplicated values
PostgreSQL - find and count duplicated values

Database preparation

create_tables.sql file:

CREATE TABLE "users" (
	"id" SERIAL PRIMARY KEY,
	"name" VARCHAR(100) NOT NULL,
	"email" VARCHAR(100) NOT NULL,
	"country" VARCHAR(15) NOT NULL
);

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');

PostgreSQL - problems

PostgreSQL - find duplicated values
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