Creating a counter in PROC SQL

#1
I'm trying to create a counter column in my PROC
SQL query with the following code:

ROW_NUMBER OVER(PARTITION BY CKey ORDER BY Date) -1 AS Counter

Unfortunately, the log generates a syntax error at the ( between the R
and the P saying "expecting one of the following: ' , ' , JOIN

What am I missing here? Any assistance would be greatly appreciated.

Thanks.