mysql_query ORDER BY most existing rows

I am administrating a little webshop built in php/mysql where users can choose from a list of items and send a request about the item they like.
Everything works fine.  But now I want to have this content list sorted after the number of the most requested items (all requests are stored in table2)

details:
I have the two existing sql tables ("content" and "request_log")

table1 "content"
==========
this table contains a long list of content offered for requests from the net. It contains the following columns: "unique_id", "name", "description", ....

table1 looks like: for example:
"767","porsche911","red, good condition fast"
"893","mercedes","silver 5 years old"
"613","lexus","gold 5 doors"



table2 "request_log"
=============
the second table is used as a request table. The rows are updated dynamically after any request of the content of table1.
It contains the following columns "unique_id", "date", "requestemail", ... (unique_id of table2 corresponds with unique_id of table1).

table2 looks like: for example:
"893","23.06.2006","wanttobuymercedes@yahoo.com"
"893","21.06.2006","requestformercedes@yahoo.com"
"893","18.12.2005","mercedesrequest@hotmail.com"
"767","23.07.2005","like_porsche@gmx.com"


Normaly table1 is shown and sorted by random.
with this cmd: $sql = mysql_query(" SELECT * FROM $tabname ORDER BY rand() ");
Now I want to sort table1 after number of requests. The result should be a sorted list of the most requested content.

output should look like this:
1.) The car mercedes with ID 893 was requested 3 times
2.) The car porsche911 with ID 767 was requested 1 time
3.) The car lexus with ID 613 was requested 0 time

I am a php newbie. php.net and EE could not help me so far. And please explain your code. ;-)

Hope someone can help me. Many thanks in advance

Mathias