• 2022-06-08
    ‍设有关系R(A,B,C),与SQL语句“Select distinct A from R Where B=17;”等价的关系代数表达式为_____。‍
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      设有关系R=(A,B,C) ,与SQL语句select distinct A,C from R where B=5等价的关系代数表达式是 A: 都等价 B: 仅Ⅰ C: 仅Ⅱ D: 都不等价

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      ‏设有关系R(A,B,C),与SQL语句“Select distinct A from R Where B=17;”等价的关系代数表达式为_____。‎ A: [img=112x20]1803c72a18badba.png[/img] B: [img=50x22]1803c72a21a479b.png[/img] C: [img=73x22]1803c72a2972d8f.png[/img] D: [img=111x23]1803c72a317b53c.png[/img]

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      设有关系R(A,B,C),与SQL语句“Select distinct A from R Where B=17;”等价的关系代数表达式为_____。 A: [img=50x22]18030b11d2f5118.png[/img] B: [img=73x22]18030b11dabded7.png[/img] C: [img=112x20]18030b11e2d76f2.png[/img] D: [img=111x23]18030b11ead43f6.png[/img]

    • 3

      设有关系R(A,B,C),与SQL语句“Select distinct A from R Where B=17;”等价的关系代数表达式为_____。 A: [img=112x20]1802ebc482f5683.png[/img] B: [img=50x22]1802ebc48b2268b.png[/img] C: [img=73x22]1802ebc4934f235.png[/img] D: [img=111x23]1802ebc49b60077.png[/img]

    • 4

      设有关系R(A,B,C),与SQL语句“Select distinct A from R Where B=17;”等价的关系代数表达式为_____。 A: [img=112x20]18030b12a676de3.png[/img] B: [img=50x22]18030b12af29d3f.png[/img] C: [img=73x22]18030b12b6f26af.png[/img] D: [img=111x23]18030b12bfdcb84.png[/img]