The DAYOFYEAR function returns a number representing the day of the year (ranging from 1 to 366, where 1 is January 1st) of the date passed in the arithmetic_expression.
Supposing that we have the PEOPLE table with a Date_of_Birth field. To find out the day of the year of the date of birth for every person in PEOPLE:
SELECT DAYOFYEAR(Date_of_Birth)
FROM PEOPLE;