PostgreSQL - count rows per day

In this article, we would like to show you how to count rows per day in PostgreSQL.

Quick solution:

SELECT 
    DATE_TRUNC('day', "datetime_column1") AS "alias1", 
	COUNT("datetime_column1") AS "alias2"
FROM "table_name"
GROUP BY DATE_TRUNC('day', "datetime_column1");

Practical example

To show how to create or replace a view, we will use the following table:

Note:

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

Example

In this example, we will display the date and the number of registered users for each day.

Query:

SELECT 
    DATE_TRUNC('day', "registration_time") AS "day", 
	COUNT("registration_time") AS "number_of_users"
FROM "users"
GROUP BY DATE_TRUNC('day', "registration_time");

Result:

Database preparation

create_tables.sql file:

CREATE TABLE "users" (
	"id" SERIAL,
	"username" VARCHAR(50) NOT NULL,
	"registration_time" DATETIME NOT NULL,
	PRIMARY KEY ("id")
);

insert_data.sql file:

INSERT INTO "users"
	("username", "registration_time")
VALUES
	('Tom', '2021-01-01 11:41:31'),
	('Chris','2021-01-02 11:42:45'),
	('Jack','2021-01-03 15:13:39'),
    ('Kim','2021-01-03 15:24:51'),
    ('Marco','2021-01-04 22:35:38'),
	('Kate','2021-01-04 22:46:51'),
	('Nam','2021-01-04 22:57:37');