PHP初學者。試圖顯示UserId

Question

我正在訪問我的數據庫上的PhpMyAdmin，我所有的名字等都是正確的，但由於某種原因用戶ID不起作用。有人能指引我朝着正確的方向嗎？

我試過打印它，但沒有顯示。

<?php session_start(); 
$username = $_GET['username']; 
$password = $_GET['password']; 


// Create connection 


$con=mysqli_connect("localhost","root","","test"); 

// Check connection 
if (mysqli_connect_errno($con)) 
{ 
echo "Failed to connect to MySQL: " . mysqli_connect_error(); 
} 



$result = mysqli_query($con,"SELECT * FROM user2 where username='$username' and password='$password'"); 

$row_cnt = mysqli_num_rows($result); 
if($row_cnt >0){ 

while($row = mysqli_fetch_array($result)){ 
$UserId = $row['UserId']; 
} 
$sqlQuery2 = "SELECT ProductID, Name, Price, Description FROM product"; 

echo "Hello ".$username."<br>" .$UserId. "<br> This is a list of products"; 

$result2 = mysqli_query($con,$sqlQuery2); 

echo "<table border='1'> 
<tr> 
<th>ProductID</th> 
<th>Name</th> 
<th>Price</th> 
<th>Description</th> 
<th>View</th> 
</tr>"; 

while($row = mysqli_fetch_array($result2)) 
{ 
echo "<tr>"; 
echo "<td>" . $row['ProductID'] . "</td>"; 
echo "<td>" . $row['Name'] . "</td>"; 
echo "<td>" . $row['Price'] . "</td>"; 
echo "<td>" . $row['Description'] . "</td>"; 
echo "<td><a href=\"detailview.php?ProductID=".$row['ProductID']."\"'>Detailed View</a></td>"; 
echo "</tr>"; 
} 
echo "</table>"; 

mysqli_close($con); 
?> 
<a href="userupdatedetails.php?UserId=<?php echo $UserId ?>">Update My Details</a> 
<?php } else{ 
echo "invalid login "; } 
?> 

Answer 1

用var_dump（$ VAR），看看有什麼是變量

1支票使用它 之前，而檢查後，如果$用戶ID設置什麼是在$結果後檢查$用戶ID返回（如果條件爲假，歐VAR沒有設置..），你應該檢查$ ROW_COUNT太

你應該縮進代碼
這裏是你的代碼reindented：

<?php session_start(); 
$username = $_GET['username']; 
$password = $_GET['password']; 


// Create connection 


$con=mysqli_connect("localhost","root","","test"); 

// Check connection 
if (mysqli_connect_errno($con)) 
{ 
    echo "Failed to connect to MySQL: " . mysqli_connect_error(); 
} 



$result = mysqli_query($con,"SELECT * FROM user2 where username='$username' and password='$password'"); 

$row_cnt = mysqli_num_rows($result); 
if($row_cnt >0){ 

    while($row = mysqli_fetch_array($result)){ 
     $UserId = $row['UserId']; 
    } 
    $sqlQuery2 = "SELECT ProductID, Name, Price, Description FROM product"; 

    echo "Hello ".$username."<br>" .$UserId. "<br> This is a list of products"; 

    $result2 = mysqli_query($con,$sqlQuery2); 

    echo "<table border='1'> 
    <tr> 
    <th>ProductID</th> 
    <th>Name</th> 
    <th>Price</th> 
    <th>Description</th> 
    <th>View</th> 
    </tr>"; 

    while($row = mysqli_fetch_array($result2)) 
    { 
     echo "<tr>"; 
     echo "<td>" . $row['ProductID'] . "</td>"; 
     echo "<td>" . $row['Name'] . "</td>"; 
     echo "<td>" . $row['Price'] . "</td>"; 
     echo "<td>" . $row['Description'] . "</td>"; 
     echo "<td><a href=\"detailview.php?ProductID=".$row['ProductID']."\"'>Detailed View</a></td>"; 
     echo "</tr>"; 
    } 
    echo "</table>"; 

    mysqli_close($con); 
    ?> 
    <a href="userupdatedetails.php?UserId=<?php echo $UserId ?>">Update My Details</a> 
    <?php 
} 
else 
{ 
    echo "invalid login "; 
} 
?>