Often in PostgreSQL you may want to group query results by day.
You can use the date_trunc statement with the following basic syntax to do so:
SELECT date_trunc('day', sale_time) AS day_sold, SUM(amount) AS total
FROM products
GROUP BY day_sold
ORDER BY day_sold;
This particular example will calculate the sum of values in the amount column and group the results by the day in the sale_time column.
Note: The ORDER BY clause is optional but we include it so that the results are sorted in order by date.
The following example shows how to use this syntax in practice.
Example: How to Group Results by Day in PostgreSQL
Suppose that we create the following table named products that contains information about the number of products sold at various times at some company:
-- create table named 'products'
CREATE TABLE products (
productID INTEGER PRIMARY KEY,
sale_time TIMESTAMP,
amount INTEGER
);
-- add rows to the table
INSERT INTO products VALUES (0001, '2024-09-12 04:15:23', 33);
INSERT INTO products VALUES (0002, '2024-09-12 04:25:00', 15);
INSERT INTO products VALUES (0003, '2024-09-13 07:39:21', 20);
INSERT INTO products VALUES (0004, '2024-09-13 16:15:13', 45);
INSERT INTO products VALUES (0005, '2024-09-14 12:15:45', 50);
INSERT INTO products VALUES (0006, '2024-09-15 04:01:23', 23);
INSERT INTO products VALUES (0007, '2024-09-15 09:55:53', 30);
INSERT INTO products VALUES (0008, '2024-09-15 10:00:00', 12);
-- view all rows in table
SELECT * FROM products;
productid | sale_time | amount
-----------+---------------------+--------
1 | 2024-09-12 04:15:23 | 33
2 | 2024-09-12 04:25:00 | 15
3 | 2024-09-13 07:39:21 | 20
4 | 2024-09-13 16:15:13 | 45
5 | 2024-09-14 12:15:45 | 50
6 | 2024-09-15 04:01:23 | 23
7 | 2024-09-15 09:55:53 | 30
8 | 2024-09-15 10:00:00 | 12
Suppose that we would like to calculate the sum of values in the amount column, grouped by day.
We can use the following syntax to do so:
SELECT date_trunc('day', sale_time) AS day_sold, SUM(amount) AS total
FROM products
GROUP BY day_sold
ORDER BY day_sold;
day_sold | total
---------------------+-------
2024-09-12 00:00:00 | 48
2024-09-13 00:00:00 | 65
2024-09-14 00:00:00 | 50
2024-09-15 00:00:00 | 65
The resulting table shows the sum of values from the amount column in the original table, grouped by day.
For example, from the output we can see:
- A total of 48 sales were made in 2024-09-12.
- A total of 65 sales were made in 2024-09-13.
- A total of 50 sales were made in 2024-09-14.
- A total of 65 sales were made in 2024-09-15.
Feel free to use similar syntax to group the results of your own query by day.
Additional Resources
The following tutorials explain how to perform other common tasks in PostgreSQL:
PostgreSQL: How to Select Rows in Date Range
PostgreSQL: How to Calculate Difference Between Rows
PostgreSQL: How to Extract Hours and Minutes from Timestamp
