DAYOFWEEK() returns the day of the week as a number.

Please note sunday equals 1 and saturday would equal 7. See full list below

Monday = 2
Tuesday = 3
Wednesday = 4
Thursday = 5
Friday = 6
Saturday = 7
Sunday = 1

Example

SELECT DAYOFWEEK( '1999-02-03' )

Returns

3 (This means it is Tuesday)