高级搜索PHP，MySQL

我试图在我的网站上设置一个高级搜索，但是当用户提交他们的搜索时，如果有一个空字段，它将作为NULL发送。我不知道如何排除空参数

以下是搜索表格：

<form>
  <div class="form-group">
    <div class="col-sm-2">
      <label for="Author" class="control-label">Author</label>
    </div>
    <div class="col-sm-10">
      <input type="text" class="form-control" id="author" placeholder="Author" name="author">
    </div>
  </div>
  <div class="form-group has-feedback">
    <div class="col-sm-2">
      <label for="isbn" class="control-label">ISBN</label>
    </div>
    <div class="col-sm-10">
      <input type="text" class="form-control" id="isbn" placeholder="ISBN" name="isbn">
    </div>
  </div>
  <div class="form-group">
    <div class="col-sm-2">
      <label for="genre" class="control-label">Genre</label>
    </div>
    <div class="col-sm-10">
      <input type="text" class="form-control" id="genre" placeholder="Genre" name="genre">
    </div>
  </div>
  <div class="form-group">
    <div class="col-sm-2">
      <label for="tags" class="control-label">Tags</label>
    </div>
    <div class="col-sm-10">
      <input type="text" class="form-control" id="tags" placeholder="Tags" name="tags">
    </div>
  </div>
  <div class="form-group">
    <div class="col-sm-2">
      <label for="location" class="control-label">Location</label>
    </div>
    <div class="col-sm-10">
      <input type="text" class="form-control" id="location" placeholder="Location" name="location">
    </div>
  </div>

  <div class="form-group">
    <div class="col-sm-offset-2 col-sm-10">
      <button type="submit" name="AdvancedSearch" value="Search" class="btn btn-block btn-lg btn-primary">Search</button>

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

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首先，我觉得我应该对优先于将请求值直接注入查询字符串做出评论

您的问题的最简单解决方案如下：

<?php

$sql="select * from Book_info where user_id=$u_id";

$title = $_REQUEST['title'];
$location = $_REQUEST['location'];

if($title != null) {
    $sql .= " AND title like '%$title%'"; 
}

if($location != null) {
    $sql .= " AND location like '%$location%'";
}

//and so on...

<?php

$sql="select * from Book_info where user_id=$u_id";

$title = $_REQUEST['title'];
$location = $_REQUEST['location'];

if($title != null) {
    $sql .= " AND title like '%$title%'"; 
}

if($location != null) {
    $sql .= " AND location like '%$location%'";
}

//and so on...