錯誤在PHP中運行SQL查詢

Question

我對PHP相當陌生，學習如何使用php運行sql查詢。

到目前爲止，我寫了下面的代碼：

<?php 
     $servername="localhost"; 
     $user="root"; 
     $password="mypassword"; 
     $dbname="mydbname"; 

     //Create Connection 
     $conn=mysqli_connect($servername,$user,$password,$dbname); 


     //Check connection 
     if(!$conn) 
     { 
      die("connection failed" . mysqli_connect_error()); 
     } 

     echo "<b>Connection is Successfull.</b>"; 


      mysqli_close($conn); 
      unset($conn); 
      $sql = "SELECT * FROM users"; 

      $query=mysqli_query($conn, $sql) or die(mysql_error()) 

     ?> 

當我運行上面的代碼，它給了我下面的錯誤

連接成功。

說明：未定義變量：CONN在/index2.php在線路34上

警告：mysqli_query（）預計參數1是mysqli的，在index2.php空給定在線路34上

我嘗試了其他幾種方法，但都顯示出某種錯誤。

Answer 1

在發送查詢之前關閉連接。美中不足:)

移動

mysqli_close($conn); 
unset($conn); 

下面

$sql = "SELECT * FROM users"; 
$query=mysqli_query($conn, $sql) or die(mysql_error()) 

Answer 2

您不能關閉查詢執行之前的mysqli連接。

您必須在執行所有查詢時關閉連接。

<?php 
     $servername="localhost"; 
     $user="root"; 
     $password="mypassword"; 
     $dbname="mydbname"; 

     //Create Connection 
     $conn=mysqli_connect($servername,$user,$password,$dbname); 


     //Check connection 
     if(!$conn) 
     { 
      die("connection failed" . mysqli_connect_error()); 
     } 

     echo "<b>Connection is Successfull.</b>"; 



      $sql = "SELECT * FROM users"; 

$query=mysqli_query($conn, $sql) or die(mysql_error()) 
mysqli_close($conn); 
      unset($conn); 
     ?> 

Answer 3

$sql = "SELECT * FROM users"; 
$query=mysqli_query($conn, $sql) or die(mysqli_error($conn)); 
mysqli_close($conn); 
unset($conn); 

Answer 4

例如：

//mysql configuration 
    $server = "localhost"; 
    $dbuser = "root"; 
    $dbpw = ""; 
    $db = "db"; 
    $con = ""; 
    $con = new mysqli($server,$dbuser,$dbpw, $db); 
//get data from table 
     $sql = "SELECT * FROM users"; 
      $rs=$con->query($sql); 
      while($row = $rs->fetch_assoc()){ 
    echo $row['ID']; 
    }