If the current date is May 5, 1901, the following query returns 17 because May 5, 1901, is in the 17th month since the start of the Teradata calendar on 1900-01-01:
SELECT TD_SYSFNLIB.MONTHNUMBER_OF_CALENDAR(CURRENT_DATE);
The following query returns 17 because May 5, 1901, is in the 17th month since the start of the COMPATIBLE calendar on 1900-01-01:
SELECT TD_SYSFNLIB.MONTHNUMBER_OF_CALENDAR(DATE '1901-05-05', ’COMPATIBLE’);