评估以下CREATETABLE语句的执行结果: CREATET ABLE customers (customer_id NUMBER,customer_name VARCHAR2(25), address VARCHAR 2(25), city VARCHAR 2(25), region VARCHAR 2(25), postal_code VARCHAR 2(11), CONSTRAINT customer_id_un UNIQUE(customer_id), CONSTRAINTcustomer_name_nnNOTNULL(customer_name)); 为什么执行时此语句会失败()
- A、NUMBER数据类型要求精度值
- B、UNIQUE约束条件必须在列级定义
- C、CREATETABLE语句不定义PRIMARYKEY
- D、不能在表级定义NOTNULL约束条件
正确答案:D
答案解析:有

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