PostgreSQL - Group rows by days

In this article, we would like to show you how in the group rows by days in PostgreSQL.

Note: at the end of this article you can find database preparation SQL queries.

SQL example:

SELECT
    DATE_TRUNC('day', "event_timestamp") AS "day",
    COUNT(*)
FROM "events"
GROUP BY DATE_TRUNC('day', "event_timestamp")
ORDER BY DATE_TRUNC('day', "event_timestamp")

Result:

Shorter notation of the example above:

SELECT
    DATE_TRUNC('day', "event_timestamp") AS "day",
    COUNT(*)
FROM "events"
GROUP BY 1
ORDER BY 1

Database preparation

create_tables.sql file:

CREATE TABLE "events" (
	"id" SERIAL NOT NULL,
	"event_timestamp" TIMESTAMP NOT NULL,
	PRIMARY KEY ("id")
);

insert_data.sql file:

INSERT INTO "events" 
    ("event_timestamp")
VALUES
    ('2021-03-11 11:41:31'),
    ('2021-03-21 12:42:32'),
    ('2021-03-22 14:44:34'),
    ('2021-03-22 15:45:35'),
    ('2021-03-23 16:46:36'),
    ('2021-04-05 17:47:37'),
    ('2021-04-05 19:49:39'),
    ('2021-04-16 20:50:40'),
    ('2021-04-17 15:45:35'),
    ('2021-04-23 16:46:36'),
    ('2021-04-23 19:49:39'),
    ('2021-04-23 20:50:40');