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Which three statements about subqueries are true? （）
A:A main query can have more than one subquery.
B:A subquery can have more than one main query.
C:The subquery and main query must retrieve data from the same table.
D:The subquery and main query can retrieve data from different tables.
E:Only one column or expression can be compared between the subquery and main query.
F:Multiple columns or expression can be compared between the subquery and main query.

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出自：Oracle认证

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