Hi hayes029, your idea was very helpful.
Here go a adaptation for select form field.
<?php
$consulta = "select * from schema.table";
$resposta = odbc_exec($con, $consulta);
for($i=1; $i <= odbc_num_fields($resposta); $i++)
echo "<option value=".odbc_field_name($resposta, $i).">".odbc_field_name($resposta, $i)."</option>";
?>