Re: Deadly sins againts database performance/scalability

Cris Carampa wrote:

> Alkos wrote:
>
> > Most of the time, people use SELECT DISTINCT to get unique rows because
> > they don't want to "bother" with the datamodel. They are lazy or 
> > hurried so
> > they don't care about possible
> > keys, about WHERE clauses selectivity and all that kind of things so 
> > quick
> > and dirty solution to be sure to get unique rows : SELECT DISTINCT which
> > implies a sort therefore more activity to get the same result as they may
> > have gotten quicker with a little bit work on the WHERE clause.
>
>
> I do use SELECT DISTINCT when I have just to pick up distinct values 
> from a table, and I don't need to count them or performing group 
> functions amongs columns in the table. I assume the performance of this 
> statement:
>
> SELECT DISTINCT FOOCOL FROM FOOTAB ;
>
> is better than the performance of this one:
>
> SELECT FOOCOL, COUNT(FOOCOL) FROM FOOTAB GROUP BY FOOCOL ;
>
> Or am I wrong?
Consider

select distinct e.first_name
from employees e, departments d;

versus

select e.first_name
from employees e, departments d
where e.department_id=d.department_id;

Oversimplified, of course, but it's the idea.
--
Regards, Frank van Bortel