question 2
view the Exhibit and examine the description of the CUSTOMERS table.You want to add a constraint on the CUST_FIRST_NAME column of the CUSTOMERS table so that the value inserted in the column does not have numbers. Which SQL statement would you use to accomplish the task?
- A.ALTER TABLE CUSTOMERS ADD CONSTRAINT cust_f_name CHECK(REGEXP_LIKE(cust_first_name,'^A-Z')) NOVALIDATE;
- B.ALTER TABLE CUSTOMERS ADD CONSTRAINT cust_f_name CHECK(REGEXP_LIKE(cust_first_name,'[1]')) NOVALIDATE;
- C.ALTER TABLE CUSTOMERS ADD CONSTRAINT cust_f_name CHECK(REGEXP_LIKE(cust_first_name,'[[:alpha:]]')) NOVALIDATE;
- D.ALTER TABLE CUSTOMERS ADD CONSTRAINT cust_f_name CHECK(REGEXP_LIKE(cust_first_name,'[[:digit:]]')) NOVALIDATE;
Correct Answer C
查看图例中对表CUSTOMERS 的定义和描述。你想给表CUSTOMERS的CUST_FIRST_NAME字段添加约束，以实现插入到表的数据中该字段不含有数字。以下哪个sql语句可以实现上述功能？
正确答案：C
解析：
本题考察的是REGEXP_LIKE以及正则表达式的用法。以下是oracle官方文档中对REGEXP_LIKE的说明。
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REGEXP_LIKE is similar to the LIKE condition, except REGEXP_LIKE performs regular expression matching instead of the simple pattern matching performed by LIKE. This condition evaluates strings using characters as defined by the input character set.
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This condition complies with the POSIX regular expression standard and the Unicode Regular Expression Guidelines.
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REGEXP_LIKE使用正则表达式进行匹配，而不是执行简单的模式匹配，除此之外，它的用法和LIKE类似。这个条件使用输入字符串的定义字符集作为评估使用的字符集。
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这个条件符合POSIX正则表达式标准和Unicode正则表达式的指导方针。
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此题使用字符簇进行匹配，常用字符簇标准如下表：
- 答案A：以大写字幕开头，B：不以数字开头，C：只包含字母，D：只包含数字。故答案C正确。
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