Php 注意问题：未定义索引

我对以下代码片段有问题：

<div class= "main2" id ="main">
<fieldset id ='fs3'>
<form action ="<?=$_SERVER['PHP_SELF']?>" method="post">
<?php

$query = pg_query($connect, "Select name FROM types") or die("");
$numrows = pg_num_rows($query);
if ($numrows > 0) {

    echo "<br /><legend><center>Some Text:</center></legend><br />";
    echo "<center>Some Text: <select name='querySelect'>";


        while($r = pg_fetch_assoc($query)) {
            echo "<option value = ".$r['name'].">".$r['name']."</option>";
                }
    echo "</select>\t";
    echo "<input type='submit' value='submit' name='submit'>";
    echo "<br />"; 
    echo "<br />"; 
    if (isset($_POST['submit'])) { 

    $querySelect = $_GET['querySelect'];
switch($querySelect)
{
    case 'A':
        $query = pg_query($connect, "Select model FROM urzadzenia WHERE tid=1") or die("");
        break;
    case 'B':
        $query = pg_query($connect, "Select model FROM urzadzenia WHERE tid=2") or die("");
        break;
    case 'C':
        $query = pg_query($connect, "Select model FROM urzadzenia WHERE tid=3") or die("");
        break;
    case 'D':
        $query = pg_query($connect, "Select model FROM urzadzenia WHERE tid=4") or die("Zapytanie nie działa");
        break;
    case 'E':
        $query = pg_query($polacz, "Select model FROM urzadzenia WHERE tid=5") or die("");
        break;  
}
}   
else
    echo "error";

}



echo "</form>";
echo "</fieldset>"
?>

在以下行中替换“按邮件获取”：

$querySelect = $_GET['querySelect'];

在以下行中替换“按邮件获取”：

$querySelect = $_GET['querySelect'];

您正在以POST方式发送数据，但正在尝试从GET获取数据

$querySelect = $_GET['querySelect'];

应该是

$querySelect = $_POST['querySelect'];

更好的是

$querySelect = !empty($_POST['querySelect']) ? $_POST['querySelect'] : null;

您正在以POST方式发送数据，但正在尝试从GET获取数据

$querySelect = $_GET['querySelect'];

应该是

$querySelect = $_POST['querySelect'];

更好的是

$querySelect = !empty($_POST['querySelect']) ? $_POST['querySelect'] : null;

$querySelect=$\u POST['querySelect']；不起作用，但你的第二个建议很有效！谢谢。不要使用空函数。如果参数包含“0”，则认为该参数为空，但您可能需要“0”。您应该使用isset，比如
$querySelect=isset（$\u POST['querySelect']）$_POST['querySelect']：空$querySelect=$\u POST['querySelect']；不起作用，但你的第二个建议很有效！谢谢。不要使用空函数。如果参数包含“0”，则认为该参数为空，但您可能需要“0”。您应该使用isset，比如
$querySelect=isset（$\u POST['querySelect']）$_POST['querySelect']：空