FROM_DAYS

Description

The FROM_DAYS function is used to convert an integer number of days to the corresponding date (DATE type). This function uses "January 1st, year 1" as the reference point (i.e., day 0 corresponds to 0000-01-01), calculating the date after the specified number of days from the reference date.

Note: To maintain behavioral consistency with MySQL, the FROM_DAYS function does not support "February 29th, year 1" (0000-02-29), even though theoretically this year conforms to leap year rules, this date will be automatically skipped. Historical date limitation: This function calculates based on the extended Gregorian calendar, and is not suitable for dates before the Gregorian calendar was introduced in 1582 (when the Julian calendar was actually used), which may cause discrepancies between results and actual historical dates.

This function behaves consistently with the from_days function in MySQL

Syntax

FROM_DAYS(<days>)

Parameters

Parameter	Description
<days>	Input number of days, of type INT

Return Value

Returns a DATE type value in the format YYYY-MM-DD, representing the date after days from the reference date (0000-01-01). If days is negative, returns NULL. If days exceeds the valid date range (typically 1 to 3652424, corresponding to approximately year 10000), returns an error.

Examples

---Calculate days from the reference date
select from_days(730669),from_days(5),from_days(59), from_days(60);

+-------------------+--------------+---------------+---------------+
| from_days(730669) | from_days(5) | from_days(59) | from_days(60) |
+-------------------+--------------+---------------+---------------+
| 2000-07-03        | 0000-01-05   | 0000-02-28    | 0000-03-01    |
+-------------------+--------------+---------------+---------------+

---If the input parameter is negative, an error is returned
select from_days(-60);
ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.3)[E-218]Operation from_days of -60 out of range

---If the input is NULL, returns NULL
select from_days(NULL);
+-----------------+
| from_days(NULL) |
+-----------------+
| NULL            |
+-----------------+

---If days exceeds the valid date range (typically 1 to 3652424, corresponding to approximately year 10000), an error is returned
select from_days(99999999);
ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.3)[E-218]Operation from_days of 99999999 out of range