Single-row functions can be used in the WHERE and HAVING clauses without requiring a subquery.
However, aggregate functions, which operate on many rows to give one result per group, cannot be used in a WHERE clause unless a subquery is used because the WHERE clause is processed before the individual rows are aggregated into groups.
A). False. Single-row functions can be directly used in the WHERE clause.
B). False. Single-row functions can be directly used in the HAVING clause.
C). True. Aggregate functions cannot be used in the WHERE clause without a subquery because the WHERE clause filters individual rows before they are aggregated.
D). False. Aggregate functions are intended to be used in the HAVING clause, which is specifically for filtering groups of rows after they have been aggregated, and they do not require a subquery to be used there.