给定关系R（A,B,C,D,E）与S（A,B,C,F,G），那么与表达式
等价的SQL语句如下：select （作答此空） from R, S where （）。
- A.R.A，R.B，R.E，S.C，G
- B.R.A，R.B，D，F，G
- C.R.A，R.B，R.D，S.C，F
- D.R.A，R.B，R.D，S.C，G
正确答案及解析
正确答案
解析
本题考查关系代数运算与SQL语言的对应关系，注意本题中R与S是做自然连接操作，操作时会将R与S中相同字段名做等值连接，并将结果集去重复。所以R与S自然连接后的结果包括以下属性：R.A，R.B，R.C，D，E，F，G。关系代数选择条件为“1＜6”，即R.A＜F。关系代数投影操作条件为“1,2,4,6,7”，对应的属性为R.A，R.B，D，F，G。
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