17.View the Exhibit and examine the data in the EMPLOYEES table.

17.View the Exhibit and examine the data in the EMPLOYEES table.



You want to generate a report showing the total compensation paid to each employee to date.

You issue the following query

SQL>SELECT ename ' joined on ' hiredate', the total compensation paid is '

TO_CHAR(ROUND(ROUND(SYSDATE-hiredate)/365) * sal + comm)

"COMPENSATION UNTIL DATE"

FROM employees;

What is the outcome?

A：It generates an error because the alias is not valid.

B：It executes successfully and gives the correct output.

C：It executes successfully but does not give the correct output.

D：It generates an error because the usage of the ROUND function in the expression is not valid.

E：It generates an error because the concatenation operator can be used to combine only two items.

答案：C

解析：这道题考察的还是列的别名

A：错误，"COMPENSATION UNTIL DATE" 只要双引号括起来，空格是可以使用的

B：错误，这里说给了一个正确的输出，题目问的是显示每个雇员支付的薪酬总额，咱们先不说sal这个字段代表的是月薪、年薪还是日薪什么的，咱不管它，按照给的sql语句应该是年薪

这里的问题主要是没有处理值为null的情况，从图中可以看出smith的comm为null，那他的工资+comm最后结果也为null，

对null进行算数运算，结果为null

SQL> select 1+null a,1*null b,1/null c,'1'||null d from dual;

A          B          C D
---------- ---------- ---------- -
1

1 row selected.

C：正确

D：错误，说是round不合法，这里是可以使用的round的参数有两种，一种是number,一种是date，这里两个日期相减最后是相差的天数是number，最后除以365也是number类型，因此可以使用

E：错误，这里说的是级联操作只能最多2个，这里说的级联操作应该指的是||这个东西，这里都没有使用||使用的是空格，我测试空格是不可以的，比如下面的示例，这里暂且不管

SQL> select a b from table1;

B
----------
1
2
SQL> select a 'w' b from table1;
select a 'w' b from table1
*
ERROR at line 1:
ORA-00923: FROM keyword not found where expected