Teradata TPump’s upsert feature is a composite of UPDATE and INSERT functionality applied to a single row. Teradata TPump upsert logic is similar to that used in MultiLoad, the only other load utility with this feature. The DML statements required to execute each iteration of upsert are a single UPDATE statement, followed by a single INSERT statement.
With upsert, if the UPDATE fails because the target row does not exist, Teradata TPump automatically executes the INSERT statement. This capability can save considerable loading time by completing this operation in a single pass instead of two.