php - 为什么 PDO query() 结果的键包含表名？

Question

我像这样用 PDO 连接 mysql:

        $servername = 'localhost';
        $servername = 'localhost';
        $dbname = 'atlas';
        $table = 'homepage_pv';
        $username = 'root';
        $password = 'mysql';
        $conn = null;
        try {
            $conn = new PDO(
                "mysql:host=$servername;dbname=$dbname",
                $username,
                $password,
                array(
                    PDO::ATTR_PERSISTENT => true,
                    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                )
            );
        }
        catch(PDOException $e) {
            echo "connect to mysql failed : " . $e->getMessage();
            $conn = null;
            exit;
        }

        $result = $conn->query('SELECT * from homepage_pv')->fetchAll(PDO::FETCH_NAMED);
        echo "result=" . json_encode($result);

结果是:

result=[{"homepage_pv.id":"1","homepage_pv.datetime":"2019-08-19 22:56:26"},{"homepage_pv.id":"2","homepage_pv.datetime":"2019-08-19 22:56:28"},{"homepage_pv.id":"3","homepage_pv.datetime":"2019-08-19 23:01:58"}]

键包含表名“homepage_pv”，这不是预期的；
但是我像这样创建 PDO :

        try {
            $conn = new PDO(
                "mysql:host=$servername;",
               ...
            );
        }
        ...
        $result = $conn->query('SELECT * from atlas.homepage_pv')->fetchAll(PDO::FETCH_NAMED);
        echo "result=" . json_encode($result);

结果中的键不再包含表名，如下所示:

result=[{"id":"1","datetime":"2019-08-19 22:56:26"},{"id":"2","datetime":"2019-08-19 22:56:28"},{"id":"3","datetime":"2019-08-19 23:01:58"},{"id":"4","datetime":"2019-08-19 23:08:48"}]

在情况1中，我在创建PDO时指定了dbname，而在查询时省略了它；
在情况2中，情况恰恰相反；

那么是什么原因造成的呢？如何在创建 PDO 时指定 dbname，而结果中的键不包含表名？

Answer 1

在 fetchAll() 中使用 PDO::FETCH_ASSOC。如果您使用 PDO::FETCH_NAMED 它将返回别名。如果别名不存在，则使用表名。附上doc供您进一步引用。