[Edit]

PostgreSQL - find duplicated values in multiple columns

1 contributors

2 contributions

0 discussions

0 points

Created by:

Amir-Hashempur

607

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

Quick solution:

xxxxxxxxxx
 
SELECT 
    "column1", COUNT("column1"),
    "column2", COUNT("column2"),
    "columnN", COUNT("columnN")
FROM
    "table_name"
GROUP BY 
    "column1",
    "column2",
    "columnN"
HAVING 
    (COUNT("column1") > 1) AND 
    (COUNT("column2") > 1) AND
    (COUNT("columnN") > 1);

Practical example

Edit

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

Note:

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

Example

Edit

In this example, we will display duplicated users and countries where:

name_quantity - number of duplicated names,
country_quantity - number of duplicated countries.

Note:

This works only when both name and country in a row are duplicated.

Query:

xxxxxxxxxx
 
SELECT 
    "name", COUNT("name") AS "name_quantity",
    "country", COUNT("country") AS "country_quantity"
FROM
    "users"
GROUP BY 
    "name",
    "country"
HAVING 
       (COUNT("name") > 1) AND 
       (COUNT("country") > 1);

Result:

Note:

Notice that Chris user both name_quantity and country_quantity equals 2 because one user is from a different country.

Database preparation

Edit

create_tables.sql file:

xxxxxxxxxx
 
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:

xxxxxxxxxx
 
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');