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What is true of using group functions on columns that contain NULL values?（）
A:Group functions on columns ignore NULL values.
B:Group functions on columns returning dates include NULL values.
C:Group functions on columns returning numbers include NULL values.
D:Group functions on columns cannot be accurately used on columns that contain NULL values.
E:Group functions on columns include NULL values in calculations if you use the keyword INC_NULLS.

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出自：Oracle认证

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