When a scalar correlated subquery is specified in the SET clause, even if the UPDATE request does not have a FROM clause, Teradata Database treats the update as a joined update because of the scalar correlated subquery.
The following example requires salesumtable to be joined with salestable, and the update is done using a merge update operation via a spool.
UPDATE sales_sum_table AS sst SET total_sales = (SELECT SUM(amount) FROM sales_table AS s WHERE s.day_of_sale BETWEEN sst.period_start AND sst.period_end);