If the current date is January 5, 1901, the following query returns 52 because January 5, 1901, is in week 52 since the start of the Teradata calendar on 1900-01-01:
SELECT TD_SYSFNLIB.WEEKNUMBER_OF_CALENDAR (CURRENT_DATE);
The following query returns 53 because January 5, 1901, is in week 53 since the start of the COMPATIBLE calendar on 1900-01-01:
SELECT TD_SYSFNLIB.WEEKNUMBER_OF_CALENDAR (DATE ‘1901-01-05’, ‘COMPATIBLE’);