If the current date is January 5, 1901, the following query returns 0 because January 5, 1901, is in week 0 of January in the Teradata calendar:
SELECT TD_SYSFNLIB.WEEKNUMBER_OF_MONTH (CURRENT_DATE);
The following query returns 1 because January 5, 1901, is in week 1 of January in the ISO calendar:
SELECT TD_SYSFNLIB.WEEKNUMBER_OF_MONTH (DATE ‘1901-01-05’, ‘ISO’);