如何将两个不相关的表合并到一个sql select语句请求中。但是，这两个表都需要有用于全文搜索的match和against函数。我得到的是一个空白响应，当我执行单表sql匹配和反请求时，它可以正常工作，但当我执行两个表时就不行了。
表1:transport-only id是一个主键整数auto\ u increment，但其余的是varchar

+----+---------+-----------+--------------+
    | id | title   | type      | tags         |
    +----+---------+-----------+--------------+
    | 1  | triumph | motorbike | sport, black |
    +----+---------+-----------+--------------+
    | 2  | bmw     | car       | hatchback    |
    +----+---------+-----------+--------------+

表2:automobile--只有id是主键integer auto\ u increment，其余的是varchar

+----+-----------+-----------+------------+---------+
    | id | name      | kind      | link       | listed  |
    +----+-----------+-----------+------------+---------+
    | 1  | suzuki    | motorbike | /bike/new/ | green   |
    +----+-----------+-----------+------------+---------+
    | 2  | volkwagan | car       | /car/new/  | limited |
    +----+-----------+-----------+------------+---------+

我需要它打印出这样的内容（只是一个注解，不确定我将如何需要id-可能需要两列id\u automobile和id\u transport来引用上面的两个表）

+----+-----------+-----------+------------+--------------+
    | id | title     | type      | link       | tags         |
    +----+-----------+-----------+------------+--------------+
    | 1  | suzuki    | motorbike | /bike/new/ | green        |
    +----+-----------+-----------+------------+--------------+
    | 2  | triumph   | motorbike |            | sport, black |
    +----+-----------+-----------+------------+--------------+
    | 3  | bmw       | car       |            | hatchback    |
    +----+-----------+-----------+------------+--------------+
    | 4  | volkwagan | car       | /car/new/  | limited      |
    +----+-----------+-----------+------------+--------------+

我失败的尝试：

<table>
      <tr>
        <th>Title</th>
        <th>Type</th>
        <th>Link</th>
        <th>Tags</th>
      </tr>

    if(isset($_GET['search'])) {
        $search = $_GET['search'];
    } else {
        $search = '';
    }

    $sql = "SELECT * FROM `transport` WHERE MATCH(title, tags) AGAINST('".$search."') CROSS JOIN `automobile` WHERE MATCH(name, listed) AGAINST('".$search."')";
    $result = $conn->query($sql);

    if ($result->num_rows > 0) {
        // output data of each row
        while($row = $result->fetch_assoc()) {
            echo "<tr>";
            echo "<td>".$row["title"]."</td><td>".$row["type"]."</td><td>".$row["link"]."</td><td>".$row["tags"]."</td>";
            echo "</tr>";
        }
    } else {
        echo "0 results";
    }
    $conn->close();

    </table>

如果有任何帮助，我将不胜感激