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..

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Answer 1

Make a function, and have @dbdate varchar(8) as your input variable.

Have it return the following:

RETURN (DATEDIFF(dd, -1, convert(datetime, @dbdate, 112)) % 7)+1;

The value 112 is the sql style YYYYMMDD.

This is deterministic because the datediff does not receive a string input, if it were to receive a string it would no longer work because it internally converts it to a datetime object. Which is not deterministic.