Thats odd..
The ID column doesnt look like an auto-incrementing value.
And if this is truly the case.. then why is the PHP script looking for one?
$a=$_GET['ID'];
&
$sql = "INSERT INTO Essai VALUES('$a','$b','$c')";
regardless... if a browser is getting a 'NOT FOUND' error when attempting to access the php script.. I dont have much hope for the Arduino to be able to 'find it'. (so to speak)
Can you elaborate on this comment you made: "Only me can access the database"
Q: How so? What criteria/protocols are in place that only you (somehow) have a magic browser that logs DB entries?
I tried in my browser.. I dont see my entries in the table results you shared/posted?
I mean you posted you wanted help.. but this is getting more difficult each time I post.
The bottom line is your janky 'server/setup' is the problem.. and you cant or wont explain it.
Why are you trying to install WAMP? if you have to use that odd domain/hosting 'thing'.. what is WAMP going to offer you? (unless your just trying to test it out locally and rule out the Arduino as the problem?)