根据您的评论，您已经有了正确的基本思想，但是实现实际上可以比您得到的要简单得多。首先，你的“控制”值，即数组 $vart etc的格式称为数组结构，而使用数组结构可能会容易得多。
数组结构的问题是，当你真的想并行地沿着所有四个数组前进时，你有多个嵌套循环试图在它们上面迭代-如果你使用一个数组结构，这个问题基本上消失了。
所以把数据改成这样：

$vars = array(
    array(
        "select" => "ons",
        "compare" => "1",
        "result" => "ons"
    ),
    // etc. etc.
    array(
        "select" => "bests",
        "compare" => "2",
        "result" => "bests2"
    ),
    // ...
``` `select` 当你站在 `SELECT` 条款， `compare` 将是右手边，并且 `result` 将是数据降落的地方。
现在像这样制作循环：

foreach ($vars as $sqldata) {
$select = $sqldata->select;
$compare = $sqldata->compare;
$result = $sqldata->result;
$$result = $db->query("SELECT * FROM products WHERE $select = $compare");
}

是的，我的意思是最后一行有两美元。这会让你达到你想去的地方，但有一个警告。在输入这个之前，如果结果不是这样的话，您需要做一些事情来让目标变量存在 `$$result` 一旦你离开这个地方 `foreach` 循环。
或者在开始之前创建一个空数组，并在运行时将结果存储在该数组中。

当$v在查询字符串中时，像这样 Package 它{$v}。
您还应该重新设计阵列：

$vars = ["ons" => 1, "popa" => 1, ... ];
$results = [];
foreach($vars as $vkey => $vval){
   $results[$vkey] = $db->query("SELECT * FROM products WHERE {$vkey} = {$vval}")->fetch_assoc();
}

edited：添加了fetch\u assoc（）调用，假设只返回一行。否则，必须使用嵌套的while：

$vars = ["ons" => 1, "popa" => 1, ... ];
$results = [];
foreach($vars as $vkey => $vval){
   $results[$vkey] = [];
   $result = $db->query("SELECT * FROM products WHERE {$vkey} = {$vval}");
    while($row=$result->fetch_assoc()){
        $results[$vkey][] = $row;
    }
}

在foreach循环中，$v变量是什么？它似乎没有在任何地方定义。

"$".$t = "SELECT * FROM products WHERE $v = $v2";

在你这边触发的错误，很奇怪，因为当我在我这边运行你的代码时，我没有得到它。
在第一个数组中，添加所有字段名和值，其中ons是字段名，1是where条件的值。其他人也一样。 $key =数据库中的字段名 $value =字段名的值

// As you have different values for bests, 1, 2, 3 and for others
// If we used bests as index ex: array('bests' => 2, 'bests' => 3). The data
// will be overwritten by the next bests as they have the same index.
// 'fieldname_value' where fieldname = ons and value = 1
$vars    = array('ons_1', 'bests_1', 'bests_2', 'bests_3'); 
$results = array();
foreach ($vars as $key => $value) {

// Here I break the value which is ex: ons_1 into 
// an array(ons, 1). This will repeat for the other values.
$values = explode('_', $value);

$sql = "SELECT * FROM products WHERE $values[0] = $values[1]"; // $values[0] = fieldname $values[1] = value_of_fieldname

$result = mysqli_query($db, $sql);

if (mysqli_num_rows($result) > 0) {
    // output data of each row
    while($row = mysqli_fetch_assoc($result)) {
        $results[$value][] = $row; // Add all rows for fieldnames (ex: ons_1, bests_1, bests_2) inside $result array
    }
} 
} 

/**
 *
 * First var_dump($results); to get a clearer view of what's going on below
 *
 * The array $results contain an array of arrays 
 * Ex: $results = array ('ons_1' => array( 0 => array('class' => your_class), 'bests_1' => array( 0 => array('class' => your_class)) 
 *
 * This if line checks whether the index exist isset($results['ons_1']) and if it is not empty !empty($results['ons_1'])
 * before doing the foreach loop. It would be unecessary to do a foreach loop that will trigger an error if ons_1 does
 * not exist and has no data. This is why this check is done.
 * 
 * The foreach loop on the other hand will loop through all the data present in 'ons_1' array. var_dump($result['ons_1']); to 
 * have an idea of what's going ons. 
 *
 */

?>

<div class="grid-container container-fluid ">
    <div id="home-page" class="home-page">

     <h2 class="featured-heading-2">On Sale Now!</h2>
        <div class="home-page-onsale">
            <?php if (isset($results['ons_1']) && !empty($results['ons_1'])) { ?>

                <?php foreach ($results['ons_1'] as $key => $product) { ?>
                        <div class="<?php echo $product['class']; ?>">
                        <div class="buy-now buy"><a href="#">BUY NOW</a></div>
                        <div h4 class="read-more" onclick="rmModal(<?php echo $product['id']; ?>)"><a href="#rmModal-<?php echo $product['title']; ?>.php">READ MORE</a></div>
                        <div class="grid-col-1"><img class="featured-image img-new" src="<?php echo $product['img']; ?>"></div>
                        </div>
                <?php } ?>
            <?php }?>
        </div>

        <div class="breakpoint-3">
                    <div class="home-page-best-anime">
                        <h2 id="home-page-best-anime bpshow" class="featured-heading-2">Best Sellers</h2>
                        <div class="home-page-best-anime-row-1">
                            <?php if (isset($results['bests_1']) && !empty($results['bests_1'])) { ?>

                                <?php foreach ($results['bests_1'] as $key => $product) { ?>
                                        <div class="<?php echo $product['class']; ?>">
                                        <div class="buy-now buy"><a href="#">BUY NOW</a></div>
                                        <div h4 class="read-more" onclick="rmModal(<?php echo $product['id']; ?>)"><a href="#rmModal-<?php echo $product['title']; ?>.php">READ MORE</a></div>
                                        <div class="grid-col-1"><img class="featured-image img-new" src="<?php echo $product['img']; ?>"></div>
                                        </div>
                                <?php } ?>
                            <?php }?>
                        </div>
                        <div class="home-page-best-anime-row-2">
                            <?php if (isset($results['bests_2']) && !empty($results['bests_2'])) { ?>

                                <?php foreach ($results['bests_2'] as $key => $product) { ?>
                                        <div class="<?php echo $product['class']; ?>">
                                        <div class="buy-now buy"><a href="#">BUY NOW</a></div>
                                        <div h4 class="read-more" onclick="rmModal(<?php echo $product['id']; ?>)"><a href="#rmModal-<?php echo $product['title']; ?>.php">READ MORE</a></div>
                                        <div class="grid-col-1"><img class="featured-image img-new" src="<?php echo $product['img']; ?>"></div>
                                        </div>
                                <?php } ?>
                            <?php }?>
                        </div>
                        <div class="home-page-best-anime-row-3">
                            <?php if (isset($results['bests_3']) && !empty($results['bests_3'])) { ?>

                                <?php foreach ($results['bests_3'] as $key => $product) { ?>
                                        <div class="<?php echo $product['class']; ?>">
                                        <div class="buy-now buy"><a href="#">BUY NOW</a></div>
                                        <div h4 class="read-more" onclick="rmModal(<?php echo $product['id']; ?>)"><a href="#rmModal-<?php echo $product['title']; ?>.php">READ MORE</a></div>
                                        <div class="grid-col-1"><img class="featured-image img-new" src="<?php echo $product['img']; ?>"></div>
                                        </div>
                                <?php } ?>
                            <?php }?>
                        </div>
                    </div>

    </div>
    </div>
</div>

您的问题是，您将字符串用作行中的代码，如：

"$".$t = "SELECT * FROM products WHERE $v = $v2";

以及：

"$".$t2 = $db->query("$".$t);

您需要做的是将代码放入eval（）函数中，如下所示：

eval('$'.$t.' = "SELECT * FROM products WHERE $var$v = $v2";');

我认为你使用的所有foreach循环都会有另一个问题，因为你所有的数组都有相同数量的元素，你应该这样做：

for ($i=0; $i <count($vart) ; $i++) { 
    eval('$'.$vart[$i].' = "SELECT * FROM products WHERE $var[$i] = $var2[$i]";');
    eval("$".$vart2[$i] .'= $db->query("$".$vart[$i]);');
}

试试看，告诉我你是怎么做的