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Which two statements about subqueries are true? （）
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.

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出自：Oracle认证

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