1z0-051 Sample Question Query

Question

I saw this question at http://education.oracle.com/pls/web_prod-plq-dad/db_pages.getpage?page_id=303&p_certName=SQ1Z0_051
3. Examine the structure of the EMP table:
  EMP      
Name  Null?  Type  
EMPNO
ENAME
SALARY
COMM_PCT
NOT NULL  NUMBER(3)
VARCHAR2(25)
NUMBER(10,2)
NUMBER(4,2)
You want to generate a report that fulfills the following requirements:
1. Displays employees' names and commission amounts
2. Excludes employees who do not have a commission
3. Displays a zero for employees whose SALARY does not have a value
You issue the following SQL statement:
SQL>SELECT ename, NVL(salary * comm_pct, 0)
FROM emp
WHERE comm_pct <> NULL;
What is the outcome?
It generates an error
It executes successfully but displays no result
It executes successfully but displays results that fulfill only requirements 1 and 3
It executes successfully and displays results that fulfill all the requirementsWhen I tried answering this question, I felt this SQL statement is syntactically correct and it does the job what it is required to do.
But then, when I checked the answers given below, I saw that the answer is It executes successfully but displays no result
Without seeing or knowing the rows in table emp, how can I conclude that this query will display no result? Please advice.
Edited by: TuX4EvA on Sep 29, 2009 2:19 AM

Answer 1

TuX4EvA wrote:
SQL>SELECT ename, NVL(salary * comm_pct, 0)
FROM emp
WHERE comm_pct &lt;&gt; NULL;
Without seeing or knowing the rows in table emp, how can I conclude that this query will display no result? Please advice.Because nothing is equal or not equal to NULL. You can only have something that IS or IS NOT NULL...