php auto close the connections so why so many mysql process through php sleeping?

[blackhorse]

mysql> SHOW FULL PROCESSLIST\G

I can see that there are 100 or so sleeping process, they are all queries through php scripts.

My questions are

1) php script auto close the mysql connection, so why these mysql processes are sleeping.

2) it seems there are mysql resource available, no process running hold the the resource, why these sleeping process be called and run and go away?

3) php.ini set up the time limit, if I run command line php not through http, the time limit doesn't apply, would that be the problem my sql process through command line php sleeping?

4) any reasons, solutions and advices?

Thanks!