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【单选题】
下列对外键的表述正确的选项是( )。A.
在创建表时创建表的主外键关联，必须先创建主表，再创建从表
B.
在创建表时，对主表中的主键字段和从表中的外键字段的数据类型没有要求
C.
在创建表时创建表的主外键关联，必须先创建从表，再创建主表
D.
删除外键约束的语法格式为： ALTER TABLE 从表名 DROP FOREIGN KEY 外键字段
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