单项选择题

When defining a referential constraint between the parent table T2 and the dependent table T1, which of the following is true?（）

A.The list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.
B.The list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.
C.The list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.
D.The list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.

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单项选择题Given the following two tables: TAB1 C1 C2 A 11 B 12 C 13 TAB2 CX CY A 21 C 22 D 23 The following results are desired: C1 C2 CX CY A 11 A 21 C 13 C 22 -- --D 23 Which of the following queries will yield the desired results?（）

A.SELECT * FROM tab1 INNER JOIN tab2 ON c1=cx
B.SELECT * FROM tab1 LEFT OUTER JOIN tab2 ON c1=cx
C.SELECT * FROM tab1 FULL OUTER JOIN tab2 ON c1=cx
D.SELECT * FROM tab1 RIGHT OUTER JOIN tab2 ON c1=cx

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