A、A subquery should retrieve only one row.
B、A subquery can retrieve zero or more rows.
C、A subquery can be used only in SQL query statements.
D、Subqueries CANNOT be nested by more than two levels.
E、A subquery CANNOT be used in an SQL query statement that uses group functions.
F、When a subquery is used with an inequality comparison operator in the outer SQL statement, the column list in the SELECT clause of the subquery should contain only one column.