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单项选择题 Given the following two tables: TAB1 R1 A A A B B C C D E TAB2 R2 A A B B C C D Which of the following queries returns the following result set? RETVAL E（）

A、SELECT r1 AS retval FROM tab1 INTERSECT SELECT r2 AS retval FROM tab2

B、SELECT r1 AS retval FROM tab1 EXCEPT SELECT r2 AS retval FROM tab2

C、SELECT DISTINCT r1 AS retval FROM tab1, tab2 WHERE r1 <> r2

D、SELECT r1 AS retval FROM tab1 UNION SELECT r2 AS retval FROM tab2

  • B

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