The DAYOFWEEK function returns a number representing the day of the week (ranging from 1 to 7, where 1 is Sunday and 7 is Saturday) 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 week of the date of birth for every person in PEOPLE :
SELECT DAYOFWEEK(Date_of_Birth)
FROM PEOPLE;