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PostgreSQL - count duplicated rows

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Created by:
Dirask Admin - Marvin
1820

In this article, we would like to show you how to count duplicated rows 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 count duplicated rows, we will use the following users table:

PostgreSQL - example data used to count duplicated rows
PostgreSQL - example data used to count duplicated rows

Note:

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

Example

In this example, we will count duplicated user names.

Query:

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

Result:

PostgreSQL - count duplicated rows - result
PostgreSQL - count duplicated rows - result

Database preparation

create_tables.sql file:

CREATE TABLE "users" (
	"id" SERIAL,
	"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');

PostgreSQL - problems

PostgreSQL - count duplicated rows
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