如果输入为空，则更新数据库中的一行，同时保留其他列中的先前数据

Question

我有一个表单，用户可以通过输入学生的用户名来更新学生。但是如果用户只想更新名字并将姓氏留空，这将从 mysql 数据库中删除姓氏。

html表单：

<form class="" action="updateStudent.php" method="post">
    Username: <input type="text" name="username" value="">
    Firstname: <input type="text" name="firstname" value="">
    Lastname: <input type="text" name="lastname" value="">
     <input type="submit" name="" value="Update">
     </form>

php:

<?php
include('connection.php');
$firstname = $_POST['firstname'];
$lastname = $_POST['lastname'];
$username = $_POST['username'];
$sql = "update employee set firstname = '$firstname',
lastname = '$lastname',
where username = '$username'";

    if ($conn->query($sql) === TRUE) {
        echo "Record updated successfully";
    }

    else{
    echo "error: $sql. " . mysqli_error($conn);
    }
mysqli_close($conn);
?>

如何更改我的代码，以便当用户只想更改名字并保留姓氏时，它最终不会在数据库中为空？

Answer 1

在表单中添加这一行

<input type="text" name="lastname" value="<?php echo $lastname; ?>" />

$lastname 是结果集中的姓氏。条件是在渲染页面之前先查询记录。

Answer 2

使用 COALESCE：

UPDATE `employee`
     SET `firstname` = COALESCE($firstname, firstname),
     `lastname` = COALESCE($lastname, lastname),
     `username` = COALESCE($username, username)
WHERE `username`= '$username'

并将 value="" 留在 HTML 表单中的输入标签中。

Answer 3

我在评论中放了同样的东西， 你需要检查这个人是否只改变了它的名字 你可以这样做

include('connection.php');
$firstname = $_POST['firstname'];
$lastname = $_POST['lastname'];
$username = $_POST['username'];
/**
*  instead of checking if the input is an empty string, try to set a minimum
*  length for the string lets put it on 5
*/ 
$minLength= 5;
$sql = '';
if(strlen($lastname) > $minLength && strlen($firstname) > $minLength){
    //both have the  required length
    $sql = "update employee 
            set firstname = '$firstname',
                lastname = '$lastname',
            where username = '$username'";
} else if(strlen($firstname) > $minLength) {
    //only first name with required length
    $sql = "update employee 
            set firstname= '$firstname',
            where username = '$username'";
} else if (strlen($lastname) > $minLength) {
    //only lastname with required length 
    $sql = "update employee 
            set lastname= '$lastname',
            where username = '$username'";
} else {
    //none applied
    $sql = false;
}

if($sql){
//it's "true" if it contains something
    if ($conn->query($sql) === TRUE) {
        echo "Record updated successfully";
    } else {
        echo "error: $sql. " . mysqli_error($conn);
    }
    mysqli_close($conn);
}

但我强烈建议如果您是更新信息，在更新表单中默认情况下这些字段在表单加载时获取当前值。

Answer 4

我假设您的意思是，如果有人将输入表单字段留空，您不想更新该列。 为此，请构建一个动态查询。

<?php
include 'connection.php';
$username = $_POST['username'];
$sql = "UPDATE employee SET ";
//where username = '$username'";
$countColumns = 0; // track how many columns we are going to update
$columns = ['firstname', 'lastname']; // add more columns to this list if needed.
foreach($columns as $key ) {
    if ( ! empty($_POST[$key] ) {
        $value = $_POST[$key];
        if ( $countColumns > 0 ) $sql .= ',';
        $sql .= "  `{$key}` = '{$value}'";
        $countColumns++;
    }
}
if ( $countColumns > 0 ) {
    $sql .= " WHERE username = '{$username}'";
    if ($conn->query($sql) === TRUE) {
        echo "Record updated successfully";
    }

    else {
        echo "error: $sql. " . mysqli_error($conn);
    }
}
else {
    // Nothing to update
}
mysqli_close($conn);

Answer 5

在MySQLi 中使用准备好的语句，它们更安全，可以帮助您防止SQL 注入攻击！

要解决您的问题，您只需检查哪些值为空并设置适当的查询，如下所示：

<?php
$conn = new mysqli($servername, $username, $password, $dbname);

// check if all fields came in and if username is not empty
if(isset($_POST['username']) && !empty($_POST['username']) && isset($_POST['firstname']) && isset($_POST['lastname']))
{
   // you can use strlen($_POST['firstname']) > 2 to check if it at least has 2 characters
   if(!empty($_POST['firstname']) && empty($_POST['lastname']))
   {
       $sql = $conn->prepare("UPDATE employee SET firstname = ? WHERE username = ?";
       $sql->bind_param("ss", $_POST['firstname'], $_POST['username']);
   }
   else if(empty($_POST['firstname']) && !empty($_POST['lastname']))
   {
       $sql = $conn->prepare("UPDATE employee SET lastname = ? WHERE username = ?";
       $sql->bind_param("ss", $_POST['lastname'], $_POST['username']);
   }
   else if(!empty($_POST['firstname']) && !empty($_POST['lastname']))
   {
       $sql = $conn->prepare("UPDATE employee SET firstname = ?, lastname = ? WHERE username = ?";
       $sql->bind_param("sss", $_POST['firstname'], $_POST['lastname'], $_POST['username']);
   }

   if ($sql->execute())
   {
      echo "Record updated successfully";
   }
   else
   {
      echo "error: " . mysqli_error($conn);
   }

   $sql->close();
}

$conn->close();
?>

Answer 6

无论他们想要更新哪个，或者他们想要同时更新两者，这都应该有效。虽然我不确定您是否必须在 IF 语句中的字符串中转义单引号。

$firstname = $_POST['firstname'];
$lastname = $_POST['lastname'];
$username = $_POST['username'];

$flen = strlen($firstname);
$llen = strlen($lastname);
$c = $flen + $llen;

if ($flen>0) {
  $fname = "firstname = '$firstname'" ;
}

if ($c=2) {
  $com =  "," ;
}

if ($llen>0) {
  $lname = "lastname = '$lastname'" ;
}

$sql = "update employee set " . $fname . $com . $lname . "
where username = '$username' ";

    if ($conn->query($sql) === TRUE) {
        echo "Record updated successfully";
    }

    else{
    echo "error: $sql. " . mysqli_error($conn);
    }
mysqli_close($conn);
?>

Answer 7

我最近创建了一个表单，我需要确保填写所有字段，因此我使用以下代码确保在继续执行我的 sql 查询之前填写所有字段。可能不是最干净的，但它可以防止空字段。这样就不会留下任何空白，并且会相应地更新。

$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];

$flen = strlen($firstName);
$llen = strlen($lastName);

switch ($flen) {
  case 0:
  echo "Click Back button and please make sure to fill in all fields";
  exit;
}
switch ($llen) {
  case 0:
  echo "Click Back button and please make sure to fill in all fields";
  exit;
}