ORDER BY(SELECT ...) for what?

Question

Hi, actually i'm preparing OCE - SQL exam...
but now when i expect no more BIG surprises for me in the sql world something appear that i have not seen before(jajajaja)...
what is the use of ORDER BY clause combining it with a SELECT statement?
example:
SQL> desc pruebas
Nombre
ID
NOMBRE
EMAIL
SQL> select * from pruebas
*2 order by (select nombre from pruebas where nombre like 'w%' and rownum <=1)*
Edited by: user586516 on Nov 15, 2008 7:05 PM

Answer 1

i aggre with Rob van Wijk that the provided example doesn't make sense.
But there are situations Where an "order by select" is useful:
Sometimes you have the restriction that a select must go against excatly one table, but the ordering should be done on a column in another table.
One example is programming with Oracle forms and wanting to put DML against a datablock which is based on one table.
A typical situation is you have a table with a suggorate foreign key and you you want to sort your query by the "business key" in the lookup table.
Example from HR-scheme:
SELECT EMPLOYEE_ID,
       LAST_NAME,
       DEPARTMENT_ID
  FROM EMPLOYEES Y
ORDER BY (SELECT DEPARTMENT_NAME
            FROM DEPARTMENTS X
           WHERE X.DEPARTMENT_ID=Y.DEPARTMENT_ID
         )hope this helps