PHP SQL mysqli_num_rows（）期望参数1为mysqli_result，给定布尔值

Question

我正在尝试为表单创建搜索栏，这是我的错误所在，对不起，我是PHP的新手，我将尽力解决此问题，

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, bool given in C:\xampp\htdocs\sampleform\crud.php on line 107
0 results

这是我的SQL命令正确的代码错误吗？

 <?php
$conn = mysqli_connect($servername,$username,$password,$dbname);
        if(!$conn) /* para ma connect sa database */
        {
        die("connection failed: " . mysqli_connect_error()); /*checking if connect*/
        }
        $sql = "SELECT * FROM tbl_friends".$search;  /*dito yung SQL command*/
        $result = mysqli_query($conn,$sql);

        if(mysqli_num_rows($result) > 0)
        {
            while($row = mysqli_fetch_assoc($result))
            {
                echo "<tr><form method ='post' action ='#'>
                <td><input type ='hidden' name='id' value ='".$row['id']."'>".$row['id']."</td>
                <td><input type ='text' name='fname' value ='".$row['name']."'></td>
                <td><input type ='submit' name='edit' value ='EDIT'></td></form>
                <td><button><a href='crud.php?del=".$row['id']."'>DELETE</a></button></td>
                </tr>";
            }

        }  else {
            echo "0 results";
        }
        mysqli_close($conn);

  ?>

搜索过程

if (isset($_GET['search']))
    {
    $search = "WHERE name LIKE '%" .$_GET['search']. "%'"; 
    }else
    {
    $search = "";
}

我的示例表单中的代码

<form action="#" method="post">
  <div class="form-group" >
    <input class="form-control input-sm" placeholder="Enter Name" name="fname" type="text">
    <input type="submit"  value="ADD FRIEND" class="form-control mb-2 " name="add">
  </div>
</form>

<form  action="#" method="get">
  <div class="form-group">
    <input class="form-control input-sm" placeholder="Enter Name" name="search" type="text">
    <input type="submit"  value="SEARCH" class="form-control mb-2 ">
  </div>
</form>
<table class="table table-dark">
  <thead>
    <tr>
      <th scope="col">ID</th>
      <th scope="col">Name</th>
      <th scope="col">EDIT</th>
      <th scope="col">DELETE</th>
    </tr>
  </thead>