Day in the Week, Month, Quarter, or Year
Returns the day in the specified time period for a given date. These functions answer questions like “do we close more deals at the beginning or end of a quarter?”.
Suppose that you want to see on which day of the week most deals are closed. Use day_in_week(date).
The resulting data displays the number of opportunities closed, grouped by the day of the week that the opportunities were closed on.

It looks like most opportunities are closed on Thursday (day 5).
Returns an integer representing the day of the week for a specific date, where 1 = Sunday, 2 = Monday, etc.
Returns an integer representing the day of the month for a specific date.
Returns an integer representing the day of the quarter for a specific date.
Returns an integer representing the day of the year for a specific date.