Where and Having Clauses

Can anyone explain the difference bwtween where clause and having clause.. In many interview ...this question is asked..
please help me?

Thanks

 

just my short description, the HAVING clause is used for filter the aggregate query, example

select acolumn, count(1)
from atable
group by acolumn
having count(1) > 2

Code (markup):

but the WHERE clause is used for reguler query, example

select acolumn
from atable
where acolumn >0

Code (markup):

 

Following links might help you..

http://www.derekallard.com/blog/post/writing-sql-with-having-vs-where-clauses/
http://lists.mysql.com/mysql/134041