Php 无法将表单字段输入数据库？

我目前遇到问题，将表单字段推入数据库。以下是我的html代码：

<form action=""  method="post">
<p>Gender:</p><input type="radio" value="Male" name="gender">Male</input>
<input type="radio" value="Female" name="gender">Female</input><br>
<p>Birthday :</p>
<input type="text" placeholder="Help VITians to wish you."></input><br>
<p>Relationship :</p>
<select name="relation">
<option value="I don't want to say">I dont want to say</option>
<option value="Single">Single</option>
<option value="In a Relationship">In a Relationship</option>
</select><br><br>
<input type="submit" name="basic" value="Submit"></input>
</form>

下面是我的php代码：

<?php
  $senddata = @$_POST['basic'];

  //Password variables
  $gender = strip_tags(@$_POST['gender']);
  $birthday = strip_tags(@$_POST['birthday']);
  $relation = strip_tags(@$_POST['relation']);

  if ($senddata) {
  //If the form has been submitted ..
        //Check whether old password equals $db_password
            if (strlen($birthday) <= 4) {
             echo "Sorry! Birthday is not right! Try entering it in DD/MM/YYYY format.";
            }
            else if(empty($birthday)){
            echo "Please enter your Birthday";
            }
            else
            {
           $update_query = mysqli_query($conn,"UPDATE users SET gender='$gender', birthday='$birthday',relation='$relation' WHERE username='$user'");
           echo "Success! Your basic information has been updated!";

            }
         }
         else
         {
         }
?>

---

，但我无法进入数据库，而且我的php代码也没有在同一页面上显示错误消息。是否有任何错误？

首先在生日输入中输入名称设置数据库连接，如果未设置，我在代码中的任何位置都看不到$user。请检查first$user是否有任何值，然后按如下方式继续：

$update = mysqli_query($conn,"UPDATE `users` SET `gender`='".$gender."', `birthday`='".$birthday."',`relation`='".$relation."' WHERE `username`='".$user."'");

---

您的where条件和mysql连接也有问题

请声明$user和$conn

$user = "usernameindb";

//DATA BASE CONNECTION

$servername = "localhost";

$username = "username";

$password = "password";

$dbname = "myDB";

$conn = mysqli_connect($servername, $username, $password, $dbname);

$update_query = mysqli_query($conn,"UPDATE `users` SET `gender`='".$gender."', `birthday`='".$birthday."',`relation`='".$relation."' WHERE `username`='".$user."'");

---

它代表着成功的信息。。。或者请输入？$user来自何处？您是否声明了您的数据库连接$conn？没有名为“生日”的字段，应该是您这里有严重的SQL注入问题，请不要在未修复的情况下上线。当回答具有严重安全缺陷的问题时，重要的是不要在回答中复制它。理想情况下，应该建议一个修复方案，或者至少向OP说明他们面临的安全问题。@halfer好的，我明白了！！想想如果用户输入了撇号的性别值会发生什么？