從MySQL獲取數據時發生未定義的變量錯誤

Question

從PHP使用MySQL數據庫獲取數據時出現錯誤。

Undefined variable: result in C:\wamp\www\mbdb\Biomarkerresult1.php on line 20 
mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in C:\wamp\www\mbdb\Biomarkerresult1.php on line 20 

我的下拉列表編碼：

<select name="names" value="name"> 

<option value="Biomarker">Select a Biomarker</option> 

<option value="Diagnostic">Diagnostic</option> 

<option value="Prognsotic">Prognostic</option> 

<option value="Predictive">Predictive</option> 

下面是顯示數據：

<?php 
$con=mysqli_connect('localhost','root','','mbdb'); 
if(mysqli_errno($con)) 
{ 
    echo "Can't Connect to mySQL:".mysqli_connect_error(); 
} 

if(isset($_POST['names'])) 
{ 
    $name = $_POST['names']; 
    $fetch="SELECT * FROM metabolites WHERE Biomarker_Category = '".$name."'"; 
    $result = mysqli_query($con,$fetch); 
} 
while($row=mysqli_fetch_array($result)) 
{ 
    //----- 
} 

誰能幫助我？

Answer 1

在錯誤的端部看到：

mysqli_fetch_array（）預計參數1被mysqli_result，在C空給出：\瓦帕\ WWW \ MBDB \ Biomarkerresult1.php上線20

這使我相信你的查詢沒有返回任何內容，所以$ result被定義爲null。要檢查這一點，我會檢查$ result是否爲null，然後再嘗試while循環。

Answer 2

用你的代碼替換你的代碼，然後希望它能正常工作。

<?php 
$con=mysqli_connect('localhost','root','','mbdb'); 
if(mysqli_errno($con)) 
{ 
    echo "Can't Connect to mySQL:".mysqli_connect_error(); 
} 

if(isset($_POST['names'])) 
{ 
    $name = $_POST['names']; 
    $fetch="SELECT * FROM metabolites WHERE Biomarker_Category = '".$name."'"; 
    $result = mysqli_query($con,$fetch);//Seems to be your your posting the data, or u'r using get and post for the same form 

    while($row=mysqli_fetch_array($result)) 
    { 
     //----- 
    } 
}