In MySQL, the DAY() function is a synonym for the DAYOFMONTH() function. It’s used to return the day of the month from a date.

In this context the “day of the month” is a value between 1 and 31, or 0 for dates with a zero day part. For example, if you provide a date of 2020-05-03, the DAY() function will return 3.

Syntax

The syntax goes like this:

DAY(date)

Where date is the date value that you want the day of the month returned from.

Example

Here’s an example to demonstrate.

SELECT DAY('2020-06-18') AS 'Result';

Result:

+--------+
| Result |
+--------+
|     18 |
+--------+

If the day part has a leading zero, the leading zero is omitted from the result. Example:

SELECT DAY('2020-06-07') AS 'Result';

Result:

+--------+
| Result |
+--------+
|      7 |
+--------+

A Database Example

Here’s an example of extracting the day part from a column when running a query against a database.

USE sakila;
SELECT
  payment_date AS 'Date/Time',
  DAY(payment_date) AS 'Day of Month'
FROM payment
WHERE payment_id = 1;

Result:

+---------------------+--------------+
| Date/Time           | Day of Month |
+---------------------+--------------+
| 2005-05-25 11:30:37 |           25 |
+---------------------+--------------+

Current Date/Time

Here’s an example of extracting the day part from the current date and time (which is returned using the NOW() function).

SELECT 
    NOW(),
    DAY(NOW());

Result:

+---------------------+------------+
| NOW()               | DAY(NOW()) |
+---------------------+------------+
| 2018-06-25 18:30:44 |         25 |
+---------------------+------------+

Another way to do this is to use the CURDATE() function, which returns only the date (but not the time).

SELECT 
    CURDATE(),
    DAY(CURDATE());    

Result:

+------------+----------------+
| CURDATE()  | DAY(CURDATE()) |
+------------+----------------+
| 2018-06-25 |             25 |
+------------+----------------+