>我有一个名为分类广告的表格，它包含以下内容：
- 编号
- 标题
- 描述
- state_id
- city_id
- cat_id
这是从数据库动态填充的。
<form name="theForm" method="post" action="advanced_search.php">
<input type="submit" name="Submit" value="Search" />
<select name="categories" >
<option value=""> Select Category</option>
</select>
<select name="state" >
<option value=""> Select state</option>
</select>
<select name="city" >
<option value=""> Select city</option>
</select>
...
当我选择一个类别并单击搜索时，将显示该类别的结果。 如果我选择一个类别和一个州，那么我希望它过滤到指定的类别和州。 如果选择了城市，也应该发生同样的情况。
例如：如果我选择明尼阿波利斯市的就业类别，则搜索应过滤到该城市的所有就业。
使用下面的代码，它需要选择所有下拉列表以使过滤器正常工作。如果我想显示指定状态下类别的所有结果，该怎么办？ 如果我只想按类别筛选，该怎么办？
if (isset($_POST['Submit'])) {
$state = $_POST['state'];
$city = $_POST['city'];
$categories = $_POST['categories'];
$select = "SELECT * FROM classifieds";
$where = " WHERE ( authorized = '1')";
$where .= " AND (cat = '" . $categories . "' AND state_id = '" . $state . "' AND city_id = '" . $city . "')";
$where .= " AND (state_id = '" . $state . "' )";
$where .= " AND (city_id = '" . $city . "' )";
$q = $select . $where . ' ORDER BY date DESC';
有人可以带我完成这个吗？
仅当他们
选择了某些内容时才添加 where 子句：
$select = "SELECT * FROM classifieds";
$where = " WHERE ( authorized = '1')";
if($categories) {
$where .= " AND (cat = '" . $categories . "' )";
}
if($state) {
$where .= " AND (state_id = '" . $state . "' )";
}
if($city) {
$where .= " AND (city_id = '" . $city . "' )";
}
$q = $select . $where . ' ORDER BY date DESC';