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Node.js - PostgreSQL - find duplicated values in multiple columns
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In this article, we would like to show you how to find duplicated values in multiple columns in the PostgreSQL database using Node.js.
Note: at the end of this article you can find database preparation SQL queries.
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const { Client } = require('pg');2
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const client = new Client({4
host: '127.0.0.1',5
user: 'postgres',6
database: 'database_name',7
password: 'password',8
port: 5432,9
});10
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const fetchDuplicateCollumns = async () => {12
const query = `13
SELECT 14
"name", COUNT("name") AS "name_count",15
"country", COUNT("country") AS "country_count"16
FROM "users"17
GROUP BY "name", "country"18
HAVING (COUNT("name") > 1) AND (COUNT("country") > 1);`;19
try {20
await client.connect(); // creates connection21
const { rows } = await client.query(query); // sends query22
console.table(rows);23
} catch (error) {24
console.error(error.stack);25
} finally {26
await client.end(); // closes connection27
}28
};29
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fetchDuplicateCollumns(); Result:
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┌─────────┬─────────┬────────────┬───────────┬───────────────┐2
│ (index) │ name │ name_count │ country │ country_count │3
├─────────┼─────────┼────────────┼───────────┼───────────────┤4
│ 0 │ 'Kim' │ '2' │ 'Vietnam' │ '2' │5
│ 1 │ 'Chris' │ '2' │ 'Spain' │ '2' │6
│ 2 │ 'Tom' │ '3' │ 'Poland' │ '3' │7
└─────────┴─────────┴────────────┴───────────┴───────────────┘Note:
Notice that
Chrisuser bothandname_countequalscountry_count2because one user is from a different country.
create_tables.sql file:
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CREATE TABLE "users" (2
"id" SERIAL,3
"name" VARCHAR(100) NOT NULL,4
"email" VARCHAR(100) NOT NULL,5
"country" VARCHAR(15) NOT NULL,6
PRIMARY KEY ("id")7
);insert_data.sql file:
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INSERT INTO "users"2
("name", "email", "country")3
VALUES4
('Tom', 'tom1@email.com', 'Poland'),5
('Tom', 'tom2@email.com', 'Poland'),6
('Tom', 'tom3@email.com', 'Poland'),7
('Kim', 'kim1@email.com', 'Vietnam'),8
('Kim', 'kim2@email.com', 'Vietnam'),9
('Chris', 'chris1@email.com', 'Spain'),10
('Chris', 'chris2@email.com', 'Spain'),11
('Chris', 'chris3@email.com', 'USA');Native SQL query (used in the above example):
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SELECT "name", COUNT("name") AS "name_count"2
FROM "users"3
GROUP BY "name"4
HAVING COUNT("name") > 1