MySQL多查询-在附加SQL参数中构建

我有以下代码：

$query  .= "SELECT COUNT( ". $r ." ) AS Total, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." >=750) AS Eng, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." >=450 AND ". $r ." <=749) AS Pas, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." <=449) AS Dis
FROM  tresults;";

这是一个多查询，使用PHP，我可以查看大量实例并将数据拉回来——这很好

然而，我需要能够做的是，根据用户从下拉菜单中输入的数据，轻松地向SQL查询添加额外的参数

因此，例如，用户可能会从下拉列表中选择一个选项，然后需要将该选项附加到SQL查询中，例如：

$query  .= "SELECT COUNT( ". $r ." ) AS Total, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." >=750 AND q16 = 'Yes') AS Eng, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." >=450 AND ". $r ." <=749 AND q16 = 'Yes') AS Pass, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." <=449 AND q16 = 'Yes') AS Dis
FROM  tresults WHERE q16 = 'Yes';";

可能有一个附加，如上所述，或几个附加

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我以前从未尝试过类似的事情，所以在我深入研究之前，我想知道是否有人有任何建议？

以下是我的一般方法：

$filter = "AND q16 = 'Yes'"; //This value is dynamic depending on dropdown selection
$query  .= "SELECT COUNT( ". $r ." ) AS Total, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." >=750 " . $filter ." ) AS Eng, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." >=450 AND ". $r ." <=749 " . $filter ." ) AS Pass, 
(SELECT COUNT( ". $r ." ) FROM  tresults WHERE ". $r ." <=449 " . $filter ." ) AS Dis
FROM  tresults WHERE 1=1 " . $filter ." ;";