How to query 10 random unique records in mysql database? [duplicate]

Question

Possible Duplicate:
how to select random unique records on each execution of the SQL Query

I have database of that structure:

id int
image_name varchar(200)
category_id int

There are about 200 records, id is unique, and there are about 20 categories, and my iamges are categorized between them.

Could you help me to get a query, which will give me 10 records with UNIQUE category_ids?

Answer 1

select DISTINCT(category),id,image_name FROM images 
  WHERE id=
    (FLOOR(RAND() * 
           (SELECT COUNT(*) FROM images )
          )
    );