OCP-1Z0-051-题目解析-第13题

13. View the Exhibit and examine the structure of the PRODUCTS table.

You need to generate a report in the following format:
CATEGORIES
5MP Digital Photo Camera's category is Photo
Y Box's category is Electronics
Envoy Ambassador's category is Hardware
Which two queries would give the required output? (Choose two.)

A. SELECT prod_name q'''s category is ' prod_category CATEGORIES
FROM products;
B. SELECT prod_name q'['s ]'category is ' prod_category CATEGORIES
FROM products;
C. SELECT prod_name q'\'s\' ' category is ' prod_category CATEGORIES
FROM products;
D. SELECT prod_name q'<'s >' 'category is ' prod_category CATEGORIES
FROM products;

注意：选项中字符串之间的连接应加连接符||
Answer: CD

题目解析：
sql中字符串的两边是需要加单引号的，表示字符串的开始和结束，如果我们想在sql中输出一个实际的单引号',那么需要连续输入四个单引号''''，其中中间的两个单引号表示一个单引号。
第一个单引号：表示字符串开始
第二个单引号：表示转义，后面接的单引号转义为真正的单引号
第三个单引号：表示实际输出的单引号
第四个单引号：表示字符串结束
如：
SQL> select '''' name from dual;

N
-
'
SQL> select 'Camera''s category is Photo' name from dual;

NAME
--------------------------
Camera's category is Photo

另外Oracle还提供了一个Q-quote的表达式，来简化SQL或PLSQL中字符串的表示，其格式为q'[Camera's category is Photo]',输出为方括号中的原始字符串格式，其中方括号可以更换为其他的任意一对特殊符号，但必须是成对出现的，不可为q'[Camera's category is Photo|'。
如：
SQL> select q'[Camera's category is Photo]' name from dual;

NAME
--------------------------
Camera's category is Photo

SQL> select q'|Camera's category is 'Photo'|' name from dual;

NAME
----------------------------
Camera's category is 'Photo'

A：错误， is后面应该是两个单引号，正确的为
SELECT prod_name || q'''s category is ''|| prod_category CATEGORIES
FROM products;
B:错误，category 前面少了一个',正确的为
SELECT prod_name || q'['s ]'||'category is '||prod_category CATEGORIES FROM products;