Php mysql查询内的条件语法

如果未启用子类别选项，如何写入$qry以使“AND subcategory='$subcategory'”消失？

添加了

$subSql

var:

$category = get_option('category');

// checks to see if subcategory is enabled in the option page  
if ( get_option('enable_subcategory') == 'y' ):   

  $subcategory = get_option('subcategory');

endif;

$qry = mysql_query("SELECT car,number FROM ".$table." 
                    WHERE category = '$category' AND subcategory = '$subcategory' 
                    ORDER BY RAND() LIMIT 20");

---

这看起来很有趣，如果没有值$subSql是空的，那么很酷；）如果删除$subcategory行并将下一行更改为$subSql=“and subcategory=”，则无需额外变量即可完成此操作。获取选项（“子类别”）。"'";@站长不空也不酷。要为空，应首先定义此变量
<?

  $category = get_option('category');

  if ( get_option('enable_subcategory') == 'y' ):   // checks to see if subcategory is enabled in the option page  

  $subcategory = get_option('subcategory');
  $subSql = "AND subcategory = '$subcategory'";

  endif;

  $qry = mysql_query("SELECT car,number FROM ".$table." WHERE category = '$category' $subSql ORDER BY RAND() LIMIT 20");

?>