SQL query to update existing records and insert new

I am trying to come up with a query for ms sql to update any existing records but insert any new records.

The complexity is that I am writing a perl program that involve hashes within hashes.

Here is sample code of what some of my queries look like. This piece right now updates existing records that have a SystemNetName = ... and now I need to include inserting new records that also have SystemNetName = ... :

sub updateTest{
foreach my $table(keys %$HoH){
foreach my $field(keys %{$HoH->{$table}}){
if($table eq "CPU"){
my $CPUstatement = "Update CPU Set Name = '$HoH->{CPU}{$field}{Name}',
MaxClockSpeed = '$HoH->{CPU}{$field}{MaxClockSpeed}'
Where SystemNetName = '$HoH->{Host}{SystemNetName}' AND
CPUNumber = '$field'";

print "$CPUstatement\n";
if ($db->Sql($CPUstatement))
{
print "Error on SQL INSERT\n";
Win32::ODBC:umpError();
}
else
{
print "insert successful\n";
}
}
}
}
}

Any help will be appreciated