EN
PostgreSQL - count distinct values
0 points
In this article, we would like to show you how to count distinct values in PostgreSQL.
Quick solution:
xxxxxxxxxx1
SELECT COUNT(DISTINCT "column_name")2
FROM "table_name";xxxxxxxxxx1
SELECT COUNT("column1") AS "alias_name", "column2", "columnN"2
FROM "table_name"3
GROUP BY "columnN"4
ORDER BY COUNT("column1") DESC;To show how to count distinct values, we will use the following table:
Note:
At the end of this article you can find database preparation SQL queries.
In this example, we will count the number of unique countries in users table.
Query:
xxxxxxxxxx1
SELECT COUNT(DISTINCT("country")) AS "unique_countries"2
FROM "users";Output:
In this example, we will count the number of users in every (unique) country in descending order.
Query:
xxxxxxxxxx1
SELECT COUNT("name") AS "number of users", "country"2
FROM "users"3
GROUP BY "country"4
ORDER BY COUNT("name") DESC;Output:
create_tables.sql file:
xxxxxxxxxx1
CREATE TABLE "users" (2
"id" SERIAL,3
"name" VARCHAR(100) NOT NULL,4
"country" VARCHAR(15) NOT NULL,5
PRIMARY KEY ("id")6
)7
ENGINE=InnoDB;insert_data.sql file:
xxxxxxxxxx1
INSERT INTO "users"2
("name", "country")3
VALUES4
('Tom', 'Poland'),5
('Chris', 'Spain'),6
('Jack', 'Spain'),7
('Kim', 'Vietnam'),8
('Marco', 'Italy'),9
('Kate', 'Spain'),10
('Nam', 'Vietnam');