Concat two fields into a dropdown menu - php

Question

I am trying to simply display two fields from a table, e.g. firstname, lastname, combine them and display in a dropdown menu that can be selected, and is stored along with other data the user inputs. Below, works for one fields, but i am struggling to combine the lastname, i have tried concat but i think i did that wrong. Thanks in advance.
//Drop Down Select
$sql = "SELECT concat (firstname, lastname) as username FROM users_tbl";
$result = pg_query($sql);
echo "<select name='firstname'>";
while ($row = pg_fetch_array($result)) {
echo "<option value='" . $row['firstname'] . "'>" . $row['firstname'] ."</option>";
}
echo "</select>";
// close connection

Answer 1

Try this way:-
$sql = "SELECT concat (firstname, lastname) as username FROM users_tbl";
$result = pg_query($sql);
echo "<select name='firstname'>";
while ($row = pg_fetch_array($result)) {
echo '<option value="'.$row['username'].'" >'.$row['username'].'</option>';
}
echo "</select>";
// close connection

Answer 2

Either rely on SQL...
while ($row = pg_fetch_array($result)) {
echo "<option value='" . $row['username'] . "'</option>";
}
OR don't use CONCAT in SQL and do it with PHP:
while ($row = pg_fetch_array($result)) {
echo "<option value='" . $row['firstname'] . " " . $row['lastname'] ."'</option>";
}
but do not do both.