AND causing problems with UPDATE

[David Coombes]

i'm trying to update a table based on two values with php.
mysq sytax is as follows:

if(mysql_query("UPDATE sub_counties SET child='".$value2."' WHERE parent='".$parent."' AND child='".$value1."'"))
{
do something
}else{
log mysql_error() into a table
}

this works and updates the table but it creates an error. i presume the problem is a small one so i replaced AND with && and am still getting the same problem. the error is:

You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near $value2 at line 1.

i need to make sure that column parent='$parent' and child='$value1',
can anyone help,
cheers,
Coombes