Deterministic scalar function to get day of week for a date

Question

SQL Server, trying to get day of week via a deterministic UDF.

Im sure this must be possible, but cant figure it out.

UPDATE: SAMPLE CODE..

C         


        

Answer 1

Slightly similar approach to aforementioned solution, but just a one-liner that could be used inside a function or inline for computed column.

Assumptions:

1. You don't have dates before 1899-12-31 (which is a Sunday)
2. You want to imitate @@datefirst = 7
3. @dt is smalldatetime, datetime, date, or datetime2 data type

If you'd rather it be different, change the date '18991231' to a date with the weekday that you'd like to equal 1. The convert() function is key to making the whole thing work - cast does NOT do the trick:

((datediff(day, convert(datetime, '18991231', 112), @dt) % 7) + 1)