730部分题疑问 请大家帮忙解疑
1.Which type of key is defined on the child table to implement a referential constraint?
A. Unique keyB. Primary keyC. Foreign keyD. Composite key 答案给了B 下列哪个键能被定义在子表上，去实施参照性约束？ 为什么不是选C?-------------------------------------------------------------
2.Which of the following strings can be inserted into an XML column using XMLPARSE?
A. "
B. ""
C. ""
D. "
但是在Which of the following strings can NOT be inserted into an XML column using XMLPARSE()?
A. "D. "
" 题中 答案是A 与上一题矛盾3.Which of the following supports the XML data type?
A. A unique index
B. A composite index
C. A check constraint
D. A generated column 答案给A
但是Which of the following CREATE TABLE statements will NOT be successful?
A. CREATE TABLE t1 (c1 XML NOT NULL UNIQUE, c2 INT) B. CREATE TABLE t1 (c1 XML NOT NULL, c2 CHAR(20)) C. CREATE TABLE t1 (c1 XML CHECK (c1 IS VALIDATED), c2 INT)D. CREATE TABLE t1 (c1 XML, c2 XML) 中的答案是A 与上一题答案矛盾，而且
each XML column used has the following restrictions:
It cannot be part of any index except an XML index. It cannot be included as a column of a primary key or unique constraint.It cannot be a foreign key of a referential constraint.
大家帮忙做以上三个题？谢谢
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第1题：个人也觉得应该选C（官方书后样题答案分析里有，只是答案选项印刷有误）。 第2题： Which of the following strings can be inserted into an XML column using XMLPARSE? 选A正解， Which of the following strings can NOT be inserted into an XML column using XMLPARSE()? 应该选C 第3题：4楼已经说明。
第3题应该选择C.参考：xml columns can be referenced in a check constraint only if CHECK constraint contains the VALIDATED predicate.