Isset in if statement not resolving as aspected

Isset in if statement not resolving as aspected

Even though both $input1 and $input2 are set variables ($input1 = 1234532
and $input2 = abcdef) the ISSET in below code seems to resolve as false
causing the 'else' to execute..
if (!isset('$input1' ,('input2'))
{
$Result1 = mysql_query
(" Select var1, var2, var3
from source
where var1 = '$input1' and var2 = '$input2';
");}
else {
{
$Result1 = mysql_query
(" Select var1, var2, var3
from source
where var1 = '$input1' or var2 = '$input2';
");}
Any suggestions?