MySQL FROM_DAYS()

 The FROM_DAYS() function in MySQL is used to convert a numeric day number (as returned by the TO_DAYS() function) into a DATE value. It is helpful when working with day numbers and you need to retrieve the corresponding calendar date.

Syntax:

FROM_DAYS(n)

• n is the numeric day value (e.g., the number of days since the year 0).

Example 1: Basic Usage

SELECT FROM_DAYS(738001) AS Date;

Output:

Date
--------
2020-12-31

Example 2: Converting with TO_DAYS()

You can use TO_DAYS() to convert a date to a numeric day number and then use FROM_DAYS() to convert it back.

SELECT 
    TO_DAYS('2024-12-23') AS DayNumber,
    FROM_DAYS(TO_DAYS('2024-12-23')) AS Date;

Output:

DayNumber    Date
----------   ----------
738852       2024-12-23

Example 3: Using in a Query

CREATE TABLE Example (
    id INT AUTO_INCREMENT PRIMARY KEY,
    days INT
);

INSERT INTO Example (days) VALUES (738852), (738853), (738854);

SELECT id, days, FROM_DAYS(days) AS ConvertedDate FROM Example;

Output:

id    days      ConvertedDate
--    ------    -------------
1     738852    2024-12-23
2     738853    2024-12-24
3     738854    2024-12-25

Notes:

• The input n should be a valid numeric day number; otherwise, the function may return NULL.
• The result is affected by the sql_mode and timezone settings only if you are dealing with DATETIME or TIMESTAMP conversions. For FROM_DAYS(), the output is purely a DATE.