Natural join , join on & join using

Question

Hi
I am preparing for the IZO-051 exams .I am totally confused with the concept of joins when answering questions .
In the Oracle certification book ..HR schema example of employees and departments is given
While answering the multiple choice questions it is difficult to to choose answer !!
I wanted to know if *Join using & join on conditions yield the same result in some cases or
where there are only 1 common column between two tables * ??
for eg if the same HR schema is to be taken
QUES: Which sql statement produce the name ,department name & city of all the employees who earn more than 10,000.
The correct answer given is the query below ..
I understand the query delivers the needed result ..
select first_name ,department_name,city
from employees e
join departments d
using(department_id)
join locations l
using(location_id)
where salary > 10000;
Also the query below gives the same results but this is not the answer???
select first_name, department_name,city
from employees e join departments d on (e.department_id= d.department_id)
join locations l on (d.location_id=l.location_id)
where salary>10000;
ALSO is there any efficiency issues related to the queries??

Answer 1

Hi,
VANPERSIE wrote:
Frank Kulash wrote:
The only thing you really have to know about them is "Don't use them." >Nobody in the real world does.Dear Frank
You confuse me
why you said noboby in the real world use them?Obviously, that was hyperbolic. I haven't asked everyone in the world if they use USING or EXISTS.
I have seen a lot of code, on this forum and elsewhere, written by a large number of people I honestly think that fewer than 1 in 1000 uses either USING or NATURAL JOIN, and it is always in the context of studying for an exam, like you, or trying something the user saw in a book. I have absolutely never seen any production code that used either.
please I just want to know whyWhy are they not used? They make assumptions about the relationships between tables based entirely on column names. Those assumptions do often not reflect reality. People are liable to name their columns anything, sometimes with very good reasons, that don't match the assumptions made by USING and NATRUAL JOIN.
NATURAL JOIN is more obviious. It's common to have auditing columns such as created_date or last_modify_user in several tables. No human being would assume that these columns were designed for joining, but that's exactly what NATURAL JOIN assumes.
USING has the same problem, to a much lesser degree. If you're using 3 tables, and they all have a column named order_id, you can't use order_id to join only 2 of the tables with USING. Also, it reverses the convention of qualifying columns that are used in multiple tables. Many people regulary qualify columns (e.g. <b>d.</b>deptno); personally, I think it's a great programming practice. When you use ON, then you must qualify column names that occur in multiple tables, but when you use USING then you must not qualify the columns that occur in join conditions, but you must qualify other ambiguous columns. Most people find that very conf<b>using</b>.