use DBI;

my $dbh = DBI->connect( ... );  # get your database handle
my $sql = "select i.name, i._eid, i.num, i.val, m.code from ...".
          " where i.name = m.code and m.code = ?";  # "?" is a "placeholder"

my $sth = $dbh->prepare( $sql );

open( R, "<", $datafile_name ) or die "$datafile_name: $!\n";
while (<R>)
{
    chomp;
    my ( $ref ) = ( /^([^\t]+)/ );

    $sth->execute( $ref );  # value passed to execute() fills the placeholder

    # use one of the DBI methods for getting the query results...
}