<form id="left" action="tables.php" method="post">
    Имя:  <input type="text" name="table" />
    <input  type="submit" name="submit" value="Имя таблицы" />
</form>
<?php
if(isset($_POST['table'])) {$table = $_POST['table'];}
if ($table == '') {unset($table);}
$sql =  "select * from .$table";
$res = OCIParse($conn, $sql);
oci_execute($res);