There are four functions for converting a date to a day number:
DAYOFYEAR(date)
DAYOFMONTH(date)
DAYOFWEEK(date)
WEEKDAY(date)
DAYOFYEAR(date) returns the day of the year for a given date (in numeric format).
DAYOFYEAR(date) returns how many days since January 1 of that year.
mysql>
mysql> SELECT DAYOFYEAR(20000201);
+---------------------+
| DAYOFYEAR(20000201) |
+---------------------+
| 32 |
+---------------------+
1 row in set (0.01 sec)