Specifies the named window in an Update Window statement on which the update or insert should be performed.
The UPDATE clause specifies the named window to which the Update Window statement publishes row updates or new rows. Optionally, you can also use this clause to set an alias for the named window, which can be used in references to the window inside the SET and WHERE clauses of the Update Window statement.
Update Window Statement
SET
WHERE
ON StreamA UPDATE MyWindow AS W SET W.Column1 = TRUE;