mysql_close()期望参数1是资源,给定字符串

use*_*430 -1 php mysql ajax json

这是我的代码,它是使用json和ajax从mysql检索信息,但不知何故它不起作用,任何人都可以帮助解决这个问题?

<?php
    $host="localhost"; 
    $username="Practical4"; 
    $password="1234"; 
    $db_name="Practical4"; 

    $con=mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
    mysql_select_db("$db_name")or die("cannot select DB");

    $sql = "select * from comment where name='$name'"; 
    $result = mysql_query($sql);
    $json = array();

    if(mysql_num_rows($result)){
        while($row=mysql_fetch_row($result)){
            $json['comment'][]=$row;
        }
    }
    mysql_close($db_name);
    echo json_encode($json); 
?>
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此外,如何逐行显示每条记录?