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设在某SELECT语句的WHERE子句中，需要对Grade列的空值进行处理。下列关于空值的操作，错误的是（）。
- A、Grade IS NOT NULL
- B、Grade IS NULL
- C、Grade = NULL
- D、NOT （Grade IS NULL）
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单选题设在某SELECT语句的WHERE子句中，需要对Grade列的空值进行处理。下列关于空值的操作，错误的是（）。A
Grade IS NOT NULLB
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