很抱歉让您失望了，但解决方案比您想象的要复杂一些。如我所见，@aynber 已经提出了建议。所以，如果他写了一个答案，首先考虑他的答案是公平的。
建议
关于关注点分离：
现在让我先说，对于未来，您应该熟悉Separation of Concerns 原则。简单来说，以您的代码为例：始终将涉及访问数据库的代码（用于获取数据、更新等）与显示数据的代码（例如页面的 HTML 部分）分开。
这意味着，如果您需要从数据库中获取数据，请在网页顶部进行，并将其保存在数组中。然后只需在网页的 HTML 部分中使用这些数组，而不是像 mysqli_query 或 mysqli_fetch_assoc 等一些与 db 相关的函数。为清楚起见，请参阅我提供的代码的 HTML 部分 ( “index.php”）。
这种方法的一大优势是，您可以将整个 php 代码从页面顶部移动到 php 函数或类方法中。然后，数组将只包含调用这些函数/方法产生的数据。
以上所有陈述的要点是什么？随心所欲地使用 php 代码和网页顶部的数据，并将结果保存在 php 数组中。数组最终应该具有这样的结构，网页的 HTML 部分的工作将非常简单：读取和显示数组元素。
所以不要将 HTML 代码与 db 相关的代码混在一起。如果你这样做，那么代码太难维护了。
关于从 PHP 打印客户端代码：
您应该记住的另一个重要约定是，不要使用 php 代码打印任何客户端代码。例如。不要使用像echo "<table><tr><td>"... 这样的语句。在这种echo 的情况下，只需将要呈现的内容保存到变量中，然后根据需要将它们显示在网页的 HTML 部分中。
关于准备好的语句：
如果你需要执行带参数的sql语句，那么使用prepared statements（而不是在这种情况下mysqli::query）。它们将保护您的代码免受最终的sql injections 的影响。为了完成，在这个答案的最后，我发布了一个 index.php 的示例，使用准备好的语句而不是 mysqli::query。
问题解答：
步骤：
关于我准备的解决方案，它包括四个步骤：
- 从数据库中获取数据并将其保存到一个数组中 (
$data)。
- 首先，创建第二个数组 (
$formattedData)。然后遍历 $data 并将其项目保存到 $formattedData 中，以便它们可以很容易地显示在选定的 HTML 结构中（div 用于字母，table 用于类别）。
- 遍历
$formattedData 并在每个字母的最后一个类别行中为每个缺少的类别附加一个带有null 的项目作为类别名称。抱歉，我在这里写了一句话，但是，如果您阅读了我的代码中的 cmets，您肯定会更好地理解我的意思。
- 通过遍历
$formattedData 并读取其值，在页面的 HTML 部分显示数据。
当然，您可以根据需要优化 php 代码和/或将其分配到两三个函数中。然后你可以调用它们并将它们的返回值分配给$data 和$formattedData 变量。
注意：
如果您使用我的连接代码，请不要忘记将我的数据库凭据替换为您的。
index.php
<?php
require 'Database/dbh.php';
$sql = 'SELECT
DISTINCT Kategori,
LEFT(Kategori, 1) AS Letter
FROM kategorier
ORDER BY Kategori';
$result = mysqli_query($conn, $sql);
/*
* Fetch all data at once, into an array like this:
*
* Array
* (
* [0] => Array
* (
* [Kategori] => Artiskok
* [Letter] => A
* )
*
* [1] => Array
* (
* [Kategori] => Asiatisk
* [Letter] => A
* )
*
* [2] => Array
* (
* [Kategori] => Burger
* [Letter] => B
* )
*
* [...] => [...]
*
* )
*/
$data = mysqli_fetch_all($result, MYSQLI_ASSOC);
/*
* Free the memory associated with the result. You should
* always free your result when it is not needed anymore.
*
* @link http://php.net/manual/en/mysqli-result.free.php
*/
mysqli_free_result($result);
/*
* Close the previously opened database connection. Not really needed because
* the PHP engine closes the connection anyway when the PHP script is finished.
*
* @link http://php.net/manual/en/mysqli.close.php
*/
mysqli_close($conn);
/*
* Iterate through the fetched data and save it into a new array, with a structure suited for the
* required HTML display. To each letter, a list of category rows is assigned. The new array will
* look like this, when the maximal number of categories per category row is 2:
*
* Array
* (
* [A] => Array
* (
* [0] => Array
* (
* [0] => Aoiuoiiiu
* [1] => Aqewroiuoiiu
* )
*
* [1] => Array
* (
* [0] => Artiskok
* [1] => Asiatisk
* )
*
* [2] => Array
* (
* [0] => Azkajhsdfjkh
* )
*
* )
*
* [B] => Array
* (
* [0] => Array
* (
* [0] => Bhaskdfhjkh
* [1] => Biuzutt
* )
*
* [1] => Array
* (
* [0] => Burger
* )
*
* )
*
* [...] => [...]
*
* )
*/
$formattedData = [];
// The maximal number of categories per each category row.
$maximalNumberOfCategoriesPerCategoryRow = 2;
// The number of categories per current category row.
$numberOfCategoriesPerCurrentCategoryRow = 0;
// The index of a category row in the list of all category rows assigned to a letter.
$indexOfCurrentCategoryRow = 0;
foreach ($data as $item) {
$letter = $item['Letter'];
$category = $item['Kategori'];
if (!array_key_exists($letter, $formattedData)) {
/*
* Assign an item with the current letter as key and an array as value.
* The array holds all category rows for the current letter.
*/
$formattedData[$letter] = [];
// Reset.
$indexOfCurrentCategoryRow = 0;
// Reset.
$numberOfCategoriesPerCurrentCategoryRow = 0;
}
// Append the current category to the current category row for the current letter.
$formattedData[$letter][$indexOfCurrentCategoryRow][] = $category;
// Increment.
$numberOfCategoriesPerCurrentCategoryRow++;
/*
* If the maximal number of categories per category row is reached...
*
* @see "Modulo" operator at https://secure.php.net/manual/en/language.operators.arithmetic.php
*/
if (
$numberOfCategoriesPerCurrentCategoryRow %
$maximalNumberOfCategoriesPerCategoryRow === 0
) {
// Reset.
$numberOfCategoriesPerCurrentCategoryRow = 0;
// Increment.
$indexOfCurrentCategoryRow++;
}
}
/*
* Append an item with "null" as category for each missing category in the last
* category row of each letter. The array holding the formatted data will look
* like this, when the maximal number of categories per category row is 2:
*
* Array
* (
* [A] => Array
* (
* [...] => [...]
*
* [2] => Array
* (
* [0] => Azkajhsdfjkh
* [1] => null
* )
*
* )
*
* [B] => Array
* (
* [...] => [...]
*
* [1] => Array
* (
* [0] => Burger
* [1] => null
* )
*
* )
*
* [...] => [...]
*
* )
*/
foreach ($formattedData as $letter => $categoryRows) {
$lastCategoryRow = end($categoryRows);
$lastCategoryRowKey = key($categoryRows);
$numberOfCategoriesPerLastCategoryRow = count($lastCategoryRow);
$numberOfMissingCategoriesInLastCategoryRow = $maximalNumberOfCategoriesPerCategoryRow -
$numberOfCategoriesPerLastCategoryRow;
for ($i = 0; $i < $numberOfMissingCategoriesInLastCategoryRow; $i++) {
// Append an item with "null" as category.
$formattedData[$letter][$lastCategoryRowKey][] = null;
}
}
//=====================================================================================
//@todo Just for testing: uncomment the next two lines to display the arrays on screen.
//=====================================================================================
//echo '<pre>' . print_r($data, TRUE) . '</pre>';
//echo '<pre>' . print_r($formattedData, TRUE) . '</pre>';
//=====================================================================================
?>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=yes" />
<meta charset="UTF-8" />
<!-- The above 3 meta tags must come first in the head -->
<title>Demo</title>
<link href="custom.css" type="text/css" rel="stylesheet">
</head>
<body>
<h3>
Demo: Print a list of categories per category letter, on multiple columns.
</h3>
<?php
if ($formattedData) { /* Data exists */
foreach ($formattedData as $letter => $categoryRows) {
?>
<div class="categories-container">
<div class="letter">
<?php echo $letter; ?>
</div>
<table class="categories">
<?php
foreach ($categoryRows as $categoryRow) {
?>
<tr>
<?php
foreach ($categoryRow as $category) {
?>
<td>
<?php echo $category; ?>
</td>
<?php
}
?>
</tr>
<?php
}
?>
</table>
</div>
<?php
}
} else { /* No data */
?>
<p class="no-data">
No data found
</p>
<?php
}
?>
</body>
</html>
custom.css
body {
margin: 0;
padding: 20px;
color: #333;
}
a {
text-decoration: none;
}
.categories-container {
margin-bottom: 10px;
}
.letter {
padding: 10px;
text-align: left;
font-weight: 700;
background-color: #a0c3e5;
}
.categories {
width: 100%;
border-spacing: 1px;
border-collapse: separate;
}
.categories td {
width: 50%;
padding: 10px;
background-color: #f4f4f4;
}
.no-data {
padding: 10px;
background-color: #f4f4f4;
}
数据库/dbh.php
<?php
/*
* This page contains the code for creating a mysqli connection instance.
*/
// Db configs.
define('HOST', 'localhost');
define('PORT', 3306);
define('DATABASE', 'tests');
define('USERNAME', 'root');
define('PASSWORD', 'root');
// Error reporting.
error_reporting(E_ALL);
ini_set('display_errors', 1); /* SET IT TO 0 ON A LIVE SERVER! */
/*
* Enable internal report functions. This enables the exception handling,
* e.g. mysqli will not throw PHP warnings anymore, but mysqli exceptions
* (mysqli_sql_exception).
*
* MYSQLI_REPORT_ERROR: Report errors from mysqli function calls.
* MYSQLI_REPORT_STRICT: Throw a mysqli_sql_exception for errors instead of warnings.
*
* @link http://php.net/manual/en/class.mysqli-driver.php
* @link http://php.net/manual/en/mysqli-driver.report-mode.php
* @link http://php.net/manual/en/mysqli.constants.php
*/
$mysqliDriver = new mysqli_driver();
$mysqliDriver->report_mode = (MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
// Create a new db connection.
$conn = mysqli_connect(HOST, USERNAME, PASSWORD, DATABASE, PORT);
用于测试的数据
CREATE TABLE `kategorier` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`Kategori` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `kategorier` (`id`, `Kategori`)
VALUES
(1,'Artiskok'),
(2,'Asiatisk'),
(3,'Burger'),
(4,'Pizza'),
(5,'Asiatisk'),
(6,'Artiskok'),
(7,'Artiskok'),
(8,'Durum'),
(9,'Durum'),
(10,'Pizza'),
(11,'Chinaboks'),
(12,'Azkajhsdfjkh'),
(13,'Aoiuoiiiu'),
(14,'Aqewroiuoiiu'),
(15,'Bhaskdfhjkh'),
(16,'Biuzutt');
结果
附加内容：
这是一个如何使用准备好的语句而不是mysqli::query 获取数据的示例。请注意，我只将数据获取代码放在这里。其余代码与上述index.php页面的omolog部分相同，使用mysqli::query。
index.php
<?php
require 'Database/dbh.php';
/*
* Save the values, with which the database data will be filtered, into variables.
* These values will replace the parameter markers in the sql statement.
* They can come, for example, from a POST request of a submitted form.
*/
$letterParam1 = 'A';
$letterParam2 = 'C';
$letterParam3 = 'P';
/*
* The SQL statement to be prepared. Notice the so-called markers, e.g. the "?" signs. They
* will be replaced later with the corresponding values when using mysqli_stmt::bind_param.
*
* @link http://php.net/manual/en/mysqli.prepare.php
*/
$sql = 'SELECT
DISTINCT Kategori,
LEFT(Kategori, 1) AS Letter
FROM kategorier
WHERE
LEFT(Kategori, 1) = ?
OR LEFT(Kategori, 1) = ?
OR LEFT(Kategori, 1) = ?
ORDER BY Kategori';
/*
* Prepare the SQL statement for execution - ONLY ONCE.
*
* @link http://php.net/manual/en/mysqli.prepare.php
*/
$statement = mysqli_prepare($conn, $sql);
/*
* Bind variables for the parameter markers (?) in the SQL statement that was passed to prepare().
* The first argument of bind_param() is a string that contains one or more characters which
* specify the types for the corresponding bind variables.
*
* @link http://php.net/manual/en/mysqli-stmt.bind-param.php
*/
mysqli_stmt_bind_param($statement, 'sss'
, $letterParam1
, $letterParam2
, $letterParam3
);
/*
* Execute the prepared SQL statement. When executed any parameter markers
* which exist will automatically be replaced with the appropriate data.
*
* @link http://php.net/manual/en/mysqli-stmt.execute.php
*/
mysqli_stmt_execute($statement);
/*
* Get the result set from the prepared statement.
*
* NOTA BENE:
*
* Available only with mysqlnd ("MySQL Native Driver")! If this is not installed, then
* uncomment "extension=php_mysqli_mysqlnd.dll" in PHP config file (php.ini) and restart
* web server (I assume Apache) and mysql service. Or use the following functions instead:
* mysqli_stmt::store_result + mysqli_stmt::bind_result + mysqli_stmt::fetch.
*
* @link http://php.net/manual/en/mysqli-stmt.get-result.php
* @link https://stackoverflow.com/questions/8321096/call-to-undefined-method-mysqli-stmtget-result
*/
$result = mysqli_stmt_get_result($statement);
/*
* Fetch all data at once, into an array like this:
*
* Array
* (
* [0] => Array
* (
* [Kategori] => Artiskok
* [Letter] => A
* )
*
* [1] => Array
* (
* [Kategori] => Asiatisk
* [Letter] => A
* )
*
* [2] => Array
* (
* [Kategori] => Burger
* [Letter] => B
* )
*
* [...] => [...]
*
* )
*/
$data = mysqli_fetch_all($result, MYSQLI_ASSOC);
/*
* Free the memory associated with the result. You should
* always free your result when it is not needed anymore.
*
* @link http://php.net/manual/en/mysqli-result.free.php
*/
mysqli_free_result($result);
/*
* Close the prepared statement. It also deallocates the statement handle.
* If the statement has pending or unread results, it cancels them
* so that the next query can be executed.
*
* @link http://php.net/manual/en/mysqli-stmt.close.php
*/
mysqli_stmt_close($statement);
/*
* Close the previously opened database connection. Not really needed because
* the PHP engine closes the connection anyway when the PHP script is finished.
*
* @link http://php.net/manual/en/mysqli.close.php
*/
mysqli_close($conn);
/*
* ---------------------------------------------------------------------------------------------
* The rest of the page is identical with the omolog part of index.php, which uses mysqli::query
* ---------------------------------------------------------------------------------------------
*/
// ...