sub fingerprint {
   my ( $self, $query, $opts ) = @_;
   $opts ||= {};
   $query = lc $query;
   $query =~ s{
              (?<![\w.+-])
              [+-]?
              (?:
                \d+
                (?:[.]\d*)?
                |[.]\d+
              )
              (?:e[+-]?\d+)?
              \b
             }
             {N}gx;                             # Float/real into N
   $query =~ s/\b0(?:x[0-9a-f]+|b[01]+)\b/N/g;  # Hex/bin into N
   $query =~ s/[xb]'N'/N/g;                     # Hex/bin into N
   $query =~ s/\\["']//g;                       # Turn quoted strings into S
   $query =~ s/(["']).*?\1/S/g;                 # Turn quoted strings into S
   $query =~ s/\A\s+//;                         # Chop off leading whitespace
   $query =~ s/\s{2,}/ /g;                      # Collapse all whitespace
   $query =~ s/[\n\r\f]+/ /g;                   # Collapse newlines etc
   $query =~ s/\Ause \S+\Z/use I/;              # Abstract the DB in USE
   $query =~ s{
               \b(in|values?)\s*\(\s*([NS])\s*,[^\)]*\)
              }
              {$1($2+)}gx;      # Collapse IN() and VALUES() lists
   # Table names that end with one or two groups of digits
   $query =~ s/(?<=\w_)\d+(_\d+)?\b/$1 ? "N_N" : "N"/eg;
   if ( $opts->{prefixes} ) { # or begin with them...
      $query =~ s/\b\d+(_\d+)?(?=[a-zA-Z_])/$1 ? "N_N" : "N"/eg;
   }
   return $query;
}