//...
echo"<link><a href="nextpage.php">$table_list[$i]</a><br>";
//...

echo "...nextpage.php?tablename=$table_list[$i]...";

$_SESSION['tablename'] = $_GET['tablename'];

echo "<a href="nextpage.php?table=" . urlencode($table_list[$i]) . "">" . $table_list[$i] . "</a>";

$_SESSION["tablename"] = $_GET["table"]

//...
echo"<a href="nextpage.php?value=$table_list[$i]">$table_list[$i]</a><br>";
//...

$_SESSION['tablename']=$_GET["value"]

echo "<link><a href="nextpage.php?tablename=$table_list[i]">$table_list[$i]</a><br>";

$tablename = $_GET['tablename'];
$_SESSION['tablename'] = $tablename;