Question

我知道代码，但由于某些原因我不知道为什么它不会起作用有人可以帮助我:( 代码

<?php
$servername = "server";
$username = "Dbname";
$password = "password";
$dbname = "name";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
     die("Connection failed: " . $conn->connect_error);
}
$j=$_SERVER['REMOTE_ADDR'];

$sql123 = "SELECT FROM Ip1 (IP) WHERE IP='$j'";
if(($sql123)>0)
   {
    echo"name already exists";
   }
 else
    {
   //insert query goes here
   $ipl = $_SERVER['REMOTE_ADDR'];
         $sql = "INSERT INTO Ip1 (IP)
         VALUES ('$ipl')";
        if ($conn->query($sql) === TRUE) {
        echo "New record created successfully";
        } else {
        echo "Error: " . $sql . "<br>" . $conn->error;
           }
    }
$conn->close();
?>

即使数据库中存在相同的ip，它也始终显示“已成功创建新记录”！我试过（（mysqli_num_rows（$ conn-＆gt; query（$ sql123）））＆gt; 0）{... 我得到这个警告：mysqli_num_rows（）期望参数1是mysqli_result，给定布尔值

Answer 1

$sql123只是一个字符串，您不进行查询$conn->query($sql123)

$res = $conn->query($sql123);
if($res && mysqli_num_rows($res)>0){...

取代

if(($sql123)>0){...

Answer 2

以这种方式使用您的查询：

$sql123 = "SELECT COUNT(*) as total_num FROM Ip1 (IP) WHERE IP='$j'";
$result = $conn->query($sql123);

if(($result['total_num']) > 0){
   echo"name already exists";
}

Answer 3

您没有执行查询，您必须计算返回的结果。

尝试更改

if(($sql123)>0)

到

if((mysqli_num_rows($conn->query($sql123)))>0)

//编辑：

此外，您的查询需要更改为：

$sql123 = "SELECT IP FROM Ip1 WHERE IP='$j'";

如何使用php检查MySQL数据库中是否已存在值

3 个答案: