Почему добавляет пустые строки в бд?

<?php
$x=odbc_connect("test","test","test");
$query = "SELECT * FROM test";
$result = odbc_exec($x, $query) or die("Couldn't execute query!");
odbc_result_all($result, "align='center' BGCOLOR='#c0c0c0' border='1' width='975' height='600'");
odbc_close($x);
?>
<form method="post" action="new.php">
<center><input type=submit value=Добивать_новую_запись><center>
</form>

<?php
$stroka1=$_POST['text_f'];
$stroka2=$_POST['text_s'];
$stroka3=$_POST['text_m'];
$x=odbc_connect("test","test","test");
$res1=odbc_exec($x,"insert into test (first_name,second_name,mail) values('$stroka1', '$stroka2', '$stroka3')");
?>
<form method="post">
first_name<input type=text name=text_f value=""><br>
second_name<input type=text name=text_s value=""><br>
mail<input type=text name=text_m value=""><br>
<center><input type=submit value=Добивать_новую_запись ><center>
</form>

<?php
if (isset($_POST['text_s']) && isset($_POST['text_m']) && isset($_POST['text_f']))
{
    $stroka1=$_POST['text_f'];
    $stroka2=$_POST['text_s'];
    $stroka3=$_POST['text_m'];
    $x=odbc_connect("test","test","test");
    $res1=odbc_exec($x,"insert into test (first_name,second_name,mail) values('$stroka1', '$stroka2', '$stroka3')");
}
?>
<form method="post">
first_name<input type=text name=text_f value=""><br>
second_name<input type=text name=text_s value=""><br>
mail<input type=text name=text_m value=""><br>
<center><input type=submit value=Добивать_новую_запись ><center>
</form>