更改为（未测试）：

while ($row = mysqli_fetch_assoc($result)) {
      if (!isset($lastLetter) || $lastLetter != $row['Letter']) {
            echo "</tr></table>";
            $lastLetter = $row['Letter'];
            echo "<h2>", $row['Letter'], "</h2>";
            echo "<table><tr>";
      }
      echo "<td>" . $row['Kategori'] . "</td>";

}
希望这对您有所帮助；）
干杯
尼古拉斯

很抱歉让你失望，但解决办法比你想象的要复杂一些。如我所见，艾恩伯已经建议过了。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：
现在让我首先说，为了将来，你应该熟悉关注点分离原则。简单地说，以您的代码为例：始终将涉及数据库访问（用于获取数据、更新等）的代码与显示数据的代码（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，请在网页顶部执行，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，而不是一些与db相关的函数，如 mysqli_query ，或 mysqli_fetch_assoc 为了清楚起见，请参阅我提供的代码的html部分（“index.php”）。
这种方法的一大优点是，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？随意处理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一种结构，即网页的html部分的工作将非常简单：只读取和显示数组元素。
所以不要把html代码和db相关的代码混在一起。如果你这么做了，那么代码就很难维护了。
关于从php打印客户端代码：
将来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。e、 g.不要使用这样的语句 echo "<table><tr><td>"... . 在这个 echo 在这种情况下，只需将要呈现的内容保存到变量中，并根据需要在网页的html部分显示它们。
关于准备好的报表：
如果您需要执行带参数的sql语句，那么使用prepared语句（而不是 mysqli::query 在这种情况下）。它们将保护您的代码不受最终sql注入的影响。为了完成，在这个答案的最后我贴了一个例子 index.php 使用准备好的语句而不是 mysqli::query .

问题解决方案：

步骤：
关于我准备的解决方案，它包括四个步骤：
从数据库获取数据并将其保存到数组中( $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 这样，它们就可以很容易地显示在选定的html结构中( div 对于信件， table 对于类别）。
迭代 $formattedData 并用 null 作为每个字母最后一个类别行中缺少的每个类别的类别名称。抱歉，我在这里写了一句话，但是，如果您阅读我代码中的注解，您肯定会更好地理解我的意思。
通过迭代显示页面的html部分中的数据 $formattedData 并读取其值。
当然，您可以根据需要优化php代码和/或将其分发到两个或三个函数中。然后您可以调用它们并将它们的返回值赋给 $data 以及 $formattedData 变量。
注：
如果您使用我的连接代码，请不要忘记用您的数据库凭据替换我的数据库凭据。
索引.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>

自定义.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

其他内容：

这是一个如何使用准备好的语句而不是 mysqli::query . 注意，我只把数据获取代码放在这里。其余代码与上面的omolog部分相同 index.php 页面，使用 mysqli::query .
索引.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
 * ---------------------------------------------------------------------------------------------
 */

// ...

我建议使用definitionlist元素而不是table元素 dl ，因为它的目的是您想要的显示结果。
不过，为了解决您的问题，我建议进行一些修改。首先，请记住 DISTINCT 应用于整个列列表，而不仅仅是它旁边的列。其次， ORDER BY 在php中，从mysql排序通常比按字母顺序排序慢，而且mysql不按字母数字值排序 naturally . 最后，由于数据需要按字母顺序进行迭代，以确定在移动到下一个组之前要显示的第一个字母，因此使用 LEFT() 在mysql中，查询并不是真正需要的。

定义列表示例：https://3v4l.org/hetha

$sql = 'SELECT DISTINCT Kategori FROM kategorier;';
 $result = mysqli_query($conn, $sql);
 if ($kategorier = mysqli_fetch_all($result, MYSQLI_ASSOC)) {
    //convert array of arrays to single array - PDO supports PDO::FETCH_GROUP|PDO::FETCH_COLUMN
    $kategorier = array_column($kategorier, 'Kategori');
    //sort the resulting array as a human would
    natsort($kategorier); 
 }
 $previousLetter = null;
 ?>
<dl>
 <?php 
 foreach ($kategorier as $kategori) {
     $currentLetter = strtoupper($kategori[0]);
     if ($previousLetter !== $currentLetter) { ?>
         <dt><h2><?php echo $currentLetter; ?></h2></dt>
     <?php  } ?>
     <dd><?php echo $kategori; ?></dd>
     <?php $previousLetter = $currentLetter; 
     } ?>      
 <dl>

表格数据：

Kategori
---------
Burger
Pizza
Pizza2
Pizza3
Chinaboks
Artiskok
Durum
Asiatisk
Asiatisk2
Asiatisk20
Asiatisk3

数据库结果：（mysql将按 1, 10, 2, 20 ，不是 1, 2, 10, 20 )

[
    ['Kategori' => 'Burger'],
    ['Kategori' => 'Pizza'],
    ['Kategori' => 'Pizza2'],
    ['Kategori' => 'Pizza3'],
    ['Kategori' => 'Chinaboks'],
    ['Kategori' => 'Artiskok'],
    ['Kategori' => 'Durum'],
    ['Kategori' => 'Asiatisk'],
    ['Kategori' => 'Asiatisk2'],
    ['Kategori' => 'Asiatisk20'],
    ['Kategori' => 'Asiatisk3'],
];

排序的php数组结果：

[
    'Artiskok',
    'Artiskok2',
    'Artiskok3',
    'Artiskok20',
    'Asiatisk',
    'Burger',
    'Chinaboks',
    'Durum',
    'Pizza',
    'Pizza2',
    'Pizza3',
];

结果html输出：
注：使用 float 将从左到右排序，即。

1 | 2
3 | 4
5

/* Suggested CSS */

* {

  box-sizing: border-box;
}
dd {
  margin-left: 0;
  float: left;
  width: 50%;
}
dt {
  padding: 12px 0;
  clear: both;
}

<dl>
    <dt><h2>A</h2></dt>
    <dd>Artiskok</dd>
    <dd>Asiatisk</dd>
    <dd>Asiatisk2</dd>
    <dd>Asiatisk3</dd>
    <dd>Asiatisk20</dd>
    <dt><h2>B</h2></dt>
    <dd>Burger</dd>
    <dt><h2>C</h2></dt>
    <dd>Chinaboks</dd>
    <dt><h2>D</h2></dt>
    <dd>Durum</dd>
    <dt><h2>P</h2></dt>
    <dd>Pizza</dd>
    <dd>Pizza2</dd>
    <dd>Pizza3</dd>
<dl>

如果你想做更复杂的css样式，比如 columns 分类。可以改用嵌套列表。但是，最好在显示视图中对数据进行迭代之前对其进行组织。

嵌套列表示例：https://3v4l.org/bavgw

//...

$letters = [];
if (!empty($kategorier)) {
    $kategorier = array_column($kategorier, 'Kategori');
    //sort the resulting array as a human would
    natsort($kategorier); 

    foreach ($kategorier as $kategori) {
        $k = strtoupper($kategori[0]);
        if (!isset($letters[$k])) {
             $letters[$k] = [];
        }
        $letters[$k][] = $kategori;
    }
}
?>

<ul class="category-index">
<?php foreach ($letters as $k => $kategorier) { ?>
    <li>
        <h2><?php echo $k; ?></h2>
        <ul class="category">
        <?php foreach ($kategorier as $kategori) { ?>
            <li><?php echo $kategori; ?></li>
        <?php } ?>
        </ul>
    </li>
<?php } ?>
</ul>

结果html输出：
注意：使用 columns css定义，将从左上到右下排序。

1 | 4
2 | 5
3

/* Suggested CSS */

* {

  box-sizing: border-box;
}

ul.category-index ul,
ul.category-index {
  list-style: none;
  margin: 0;
  padding: 0;
}

ul.category-index li {
  padding: 0;
  margin: 0;
}

ul.category {
  columns: 2;
}

<ul class="category-index">
  <li>
    <h2>A</h2>
    <ul class="category">
      <li>Artiskok</li>
      <li>Asiatisk</li>
      <li>Asiatisk2</li>
      <li>Asiatisk3</li>
      <li>Asiatisk20</li>
    </ul>
  </li>
  <li>
    <h2>B</h2>
    <ul class="category">
      <li>Burger</li>
    </ul>
  </li>
  <li>
    <h2>C</h2>
    <ul class="category">
      <li>Chinaboks</li>
    </ul>
  </li>
  <li>
    <h2>D</h2>
    <ul class="category">
      <li>Durum</li>
    </ul>
  </li>
  <li>
    <h2>P</h2>
    <ul class="category">
      <li>Pizza</li>
      <li>Pizza2</li>
      <li>Pizza3</li>
    </ul>
  </li>
</ul>

至于你想要的 table 元素用法。您可以使用嵌套列表示例php代码，其中包含以下html。但是，为了确保整个表是统一的，您将需要使用单个表。 colspan="2" 可用于类别索引行，以跨两列展开它们。要确定何时需要新行， % 2 将在类别的每个偶数迭代中发生。以及使用 count 确定是否需要将空表单元格添加到当前类别列表中，并避免创建额外的空表行。

表格示例：https://3v4l.org/zun20

//...    

$letters = [];
if (!empty($kategorier)) {
    $kategorier = array_column($kategorier, 'Kategori');
    //sort the resulting array as a human would
    natsort($kategorier); 

    foreach ($kategorier as $kategori) {
        $k = strtoupper($kategori[0]);
        if (!isset($letters[$k])) {
             $letters[$k] = [];
        }
        $letters[$k][] = $kategori;
    }
}
?>
<table>
    <tbody>
    <?php foreach($letters as $k => $kategorier) { ?>
        <tr>
           <td colspan="2"><h2><?php echo $k; ?></h2></td>
        </tr>
        <tr>
        <?php 
        $l = count($kategorier);
        if ($l & 1) {
           $kategorier[] = '';
           $l++;
        }
        $y = $l - 1;
        foreach ($kategorier as $i => $kategori) { ?>
            <td><?php echo $kategori; ?></td>
            <?php if ($i % 2 && $i !== $y) { ?></tr><tr><?php } ?>
        <?php } ?>
        </tr>
    <?php } ?>
    </tbody>
</table>

生成的html:
注：使用 table 将从左到右排序。即

1 | 2
3 | 4
5 |

/* Example CSS */

* {

  box-sizing: border-box;
}

table {
  width: 100%;
}

<table>
  <tr>
    <td colspan="2">
      <h2>A</h2>
    </td>
  </tr>
  <tr>
    <td>Artiskok</td>
    <td>Asiatisk</td>
  </tr>
  <tr>
    <td>Asiatisk2</td>
    <td>Asiatisk3</td>
  </tr>
  <tr>
    <td>Asiatisk20</td>
    <td></td>
  </tr>
  <tr>
    <td colspan="2">
      <h2>B</h2>
    </td>
  </tr>
  <tr>
    <td>Burger</td>
    <td></td>
  </tr>
  <tr>
    <td colspan="2">
      <h2>C</h2>
    </td>
  </tr>
  <tr>
    <td>Chinaboks</td>
    <td></td>
  </tr>
  <tr>
    <td colspan="2">
      <h2>D</h2>
    </td>
  </tr>
  <tr>
    <td>Durum</td>
    <td></td>
  </tr>
  <tr>
    <td colspan="2">
      <h2>P</h2>
    </td>
  </tr>
  <tr>
    <td>Pizza</td>
    <td>Pizza2</td>
  </tr>
  <tr>
    <td>Pizza3</td>
    <td></td>
  </tr>
</table>

我建议您可以使用引导模板，并使用下面的代码的结果，结果将在两列分开，因为你需要。

echo "<div class="col-lg-6 col-md-6 col-sm-6"><table><tr><td>" . $row['Kategori'] . "</td></tr></table></div>";