This statement is ANSI SQL:2011 compliant, but includes non-ANSI Teradata extensions.
In the presence of an ORDER BY clause and the absence of a ROWS or ROWS BETWEEN clause, ANSI SQL:2011 window aggregate functions use ROWS UNBOUNDED PRECEDING as the default aggregation group, whereas Teradata SQL window aggregate functions use ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING.