我在向数据库添加内容时遇到问题。每次我刷新页面时，它都会再次添加完全相同的值。我怎样才能让它停止这样做？我不知道它为什么这样做。
我希望它将值添加到数据库中一次并将它们存储在那里。创建表并添加值后，将在页面上使用这些值。用户将能够添加更多值。
它还添加用户在刷新时输入的任何内容。
有问题的部分是
$db_query = 'INSERT INTO `cars`' .
' (`id`, `make`, `model`, `year`, `color`, `engine`)' .
' VALUES' .
' (NULL, ''Citroen'', ''Saxo'', ''1997'', ''White'', 1.1),' .
' (NULL, ''Citroen'', ''C3'', ''2012'', ''Blue'', 1.4),' .
' (NULL, ''Volkswagen'', ''Golf'', ''2010'', ''Blue'', 1.8),' .
' (NULL, ''Ford'', ''Mondeo'', ''2009'', ''Black'', 1.6),' .
' (NULL, ''Renault'', ''Clio'', ''2010'', ''Silver'', 1.2);';
$result = mysqli_query($conn, $db_query);
完整代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Task 7</title>
</head>
<body>
<?php
# Connection to the database start
$host = 'localhost';
$user = 'root'; # Your username
$password = 'vertrigo'; # Your password
$databaseName = 'db2'; # Your database
$conn = mysqli_connect($host, $user, $password, $databaseName);
if (mysqli_connect_errno($conn)) {
echo 'Failed to connect to MySQL: ' . mysqli_connect_error();
} else {
echo 'have connection<br>';
}
# Connection to the database end (output messages created)
# Creating the table with rows start
$db_query = 'CREATE TABLE IF NOT EXISTS `cars` (' .
'`id` int(11) NOT NULL AUTO_INCREMENT,' .
'`make` varchar(50) NOT NULL,' .
'`model` varchar(50) NOT NULL,' .
'`year` varchar(4) NOT NULL,' .
'`color` varchar(50) NOT NULL,' .
'`engine` decimal(2,1) NOT NULL,' .
'PRIMARY KEY (`id`));';
$result = mysqli_query($conn, $db_query);
# Creating table with rows end
# Putting information in each column start
$db_query = 'INSERT INTO `cars`' .
' (`id`, `make`, `model`, `year`, `color`, `engine`)' .
' VALUES' .
' (NULL, ''Citroen'', ''Saxo'', ''1997'', ''White'', 1.1),' .
' (NULL, ''Citroen'', ''C3'', ''2012'', ''Blue'', 1.4),' .
' (NULL, ''Volkswagen'', ''Golf'', ''2010'', ''Blue'', 1.8),' .
' (NULL, ''Ford'', ''Mondeo'', ''2009'', ''Black'', 1.6),' .
' (NULL, ''Renault'', ''Clio'', ''2010'', ''Silver'', 1.2);';
$result = mysqli_query($conn, $db_query);
# Putting information at each end
# Add cars START
@$cars = $_POST['cars'];
if (isset($cars)) {
$db_query = "INSERT INTO cars (make, model, year, color, engine) VALUES ('" . $cars['0'] . "','" . $cars['1'] . "','" . $cars['2'] . "','" . $cars['3'] . "','" . $cars['4'] . "')";
mysqli_query($conn, $db_query);
} else {
echo 'Cars array does not exists and obtained from FORM.';
}
# Add cars END
# Select the cars table if the right output the headers start
$db_query = "SELECT * FROM cars WHERE id <> 0 ORDER BY year ASC";
if ($result = mysqli_query($conn, $db_query)) {
echo " <table border='1'>";
echo " <tr><td>Make</td><td>Year</td><td>model</td><td>color</td><td>engine</td></tr>";
# Select cars table if the right output the headers end
# while start, output the content of the column.
while ($row = mysqli_fetch_assoc($result)) {
?>
<tr>
<td><?php echo $row['make']; ?></td>
<td><?php echo $row['year']; ?></td>
<td><?php echo $row['model']; ?></td>
<td><?php echo $row['color']; ?></td>
<td><?php echo $row['engine']; ?></td>
</tr>
<?php
}
# End while
echo "</table>";
}
?>
<form action="index.php" method="post" name="zatupok">
<fieldset>
<legend>MY CARS</legend>
<label>Make</label>
<input type="text" name="cars[]">
<label>Model</label>
<input type="text" name="cars[]">
<label>Year</label>
<input type="text" name="cars[]">
<label>Color</label>
<input type="text" name="cars[]">
<label>Engine</label>
<input type="text" name="cars[]">
<input type="submit">
</fieldset>
</form>
</body>
</html>
为什么每次访问页面时都会添加示例值
每次访问页面时都会执行您的 PHP 代码。它生成页面（动态写入页面的一部分，只是复制<?php … ?>之外的所有内容），页面是脚本的输出。Apache，或者你使用的任何服务器软件，只是获取一个HTTP请求，执行你的脚本，获取它的输出，并以HTTP响应的形式将其发送到客户端。
如果您的INSERT查询是无条件执行的（按原样），则每次访问该页面时也会执行该查询。这就是一遍又一遍地添加值的原因。
如何停止添加示例值
您可能需要检查是否已创建cars表，并仅在以下情况下执行插入查询：
# Creating the table with rows start
# CHANGED: Notice that IF NOT EXISTS is not used anymore!
# Fails if the table already exists, not touching its original contents.
$db_query = 'CREATE TABLE `cars` (' .
'`id` int(11) NOT NULL AUTO_INCREMENT,' .
'`make` varchar(50) NOT NULL,' .
'`model` varchar(50) NOT NULL,' .
'`year` varchar(4) NOT NULL,' .
'`color` varchar(50) NOT NULL,' .
'`engine` decimal(2,1) NOT NULL,' .
'PRIMARY KEY (`id`));';
$result = mysqli_query($conn, $db_query);
# Creating the table with rows end
# Putting information in each column start
$db_query = 'INSERT INTO `cars`' .
' (`id`, `make`, `model`, `year`, `color`, `engine`)' .
' VALUES' .
' (NULL, ''Citroen'', ''Saxo'', ''1997'', ''White'', 1.1),' .
' (NULL, ''Citroen'', ''C3'', ''2012'', ''Blue'', 1.4),' .
' (NULL, ''Volkswagen'', ''Golf'', ''2010'', ''Blue'', 1.8),' .
' (NULL, ''Ford'', ''Mondeo'', ''2009'', ''Black'', 1.6),' .
' (NULL, ''Renault'', ''Clio'', ''2010'', ''Silver'', 1.2);';
# CHANGED: Executing the query only if previous query (`CREATE TABLE …`) succeeded.
if ($result) {
$result = mysqli_query($conn, $db_query);
}
# Putting information at each end
开机自检问题后刷新
我们在调试问题期间遇到的另一个问题是提交 POST 表单后刷新。浏览器会自动再次提交原始表单内容，这是标准行为。它导致再次将提交的值插入数据库，现在将它们存储在两个甚至更多副本中。
不过，这是可以防止的。例如，请参阅停止浏览器要求在刷新时重新发送表单数据。接受的答案推荐 POST-redirect-GET 模式，这是我在您的情况下会使用的模式。谷歌搜索时，您可以获得有关该主题的更多信息 post data resent stackoverflow .