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【多选题】
下列关于关系数据库的叙述，正确的是（）A.
关系模型是目前在数据库管理系统中使用最为广泛的数据模型
B.
关系模型反映二维表的内容，而关系反映二维表的静态结构
C.
关系是一种规范化二维表中行的集合
D.
常用的关系操作有并、交、差、插入、更新、删除、选择、投影和连接等
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