Print each of the values before you do anything, and see which one doesn't have a value. Figure out why that variable doesn't have a value and you'll figure out how to get rid of that warning.

What is the $_[$_-1] supposed to do? Do you really mean to use a global variable, $_, like that?

Just a minor style comment, this style of argument handling is a little bit unusual. Generally this would look like:

sub queryDBI {
  my ($foo,$bar,$baz,$table)=@_;
  my $query="Select $foo, $bar, $baz from $table";
[download]

Directly accessing @_ is ugly and confusing and suffers from the problem that if you change the order of arguments or perhaps add a new argument somewhere in the middle making the appropriate changes is quite error prone. People occasionally do it in "tiny subs" and gurus will occasionally resort to it for their own purposes (remember @_ is magic) but to see it in code like this is a bad sign. Use named lexical copies of the arguments instead.

# Access directly the last element of the array
sub queryDBI {
    my $query1 = "SELECT $_[2],$_[3],$_[-1] FROM " . $_[1];
    return $query1;
} 
print queryDBI(qw/first second third fourth fifth_and_last/),$/ x 2'
[download]

# In scalar context, @array returns the number of elements in contains
+.
# As @array indexes start at 0 (unless someone explicitly changes this
+ through $[), we substract 1
sub queryDBI {
    my $query1 = "SELECT $_[2],$_[3],$_[@_-1] FROM " . $_[1];
    return $query1;
} 
print queryDBI(qw/first second third fourth fifth_and_last/),$/ x 2'
[download]

# $#array returns the index of the last element of the array.
sub queryDBI {
    my $query1 = "SELECT $_[2],$_[3],$_[$#_] FROM " . $_[1];
    return $query1;
} 
print queryDBI(qw/first second third fourth fifth_and_last/),$/ x 2'
[download]

Dave.