php - 警告 : Invalid argument supplied for foreach() when retrieving data from database

Question

我试图从两个表中检索数据并回显结果，sql 似乎是正确的，但它告诉我参数无效。这是我的代码:

// Retrieve all information related to this post
    function get_post_data($post_id){

        //test the connection
        try{
            //connect to the database
            $dbh = new PDO("mysql:host=localhost;dbname=mjbox","root", "usbw");
        //if there is an error catch it here
        } catch( PDOException $e ) {
            //display the error
            echo $e->getMessage();
        }

        $sql = 'SELECT * FROM mjbox_images JOIN mjbox_posts USING (post_id) WHERE post_id = $post_id';
        $result = $dbh->query( $sql );

        foreach($result as $row):

            echo $row['img_id'];

        endforeach;

    }

Answer 1

查询中的 $post_id 不会被扩展，因为该字符串是单引号的。

它应该可以更好地配合:

$sql = "SELECT * FROM mjbox_images JOIN mjbox_posts USING (post_id) WHERE post_id = $post_id";

或者:

$sql = 'SELECT * FROM mjbox_images JOIN mjbox_posts USING (post_id) WHERE post_id = '.$post_id;