PHP连接不起作用吗？

Question

我不能正确地拼接，它根本就不能工作：

这不是对的吗？我尝试将变量放在select查询中，并回显$firstname。

<?php $user = $_SESSION["UserID"];?>

<?php
$user = $_SESSION["UserID"]; 

function getFirstname($db) {
    $firstname=false;
    $sql = "SELECT firstname FROM Users WHERE username = '$user'";
    foreach ($db->query($sql) as $row) {
        $firstname=$row['firstname'];
    }
    return $firstname;
}

$firstname=getFirstname( $db );
?>


<?php echo $firstname  ?>

它似乎不会输出名字。

Answer 1

您要么将$user传递给函数，要么将全局$user设置为函数，如下所示，代码和(.)用于连接

function getFirstname($db) {
     global $user;
    $firstname=false;
    $sql = "SELECT firstname FROM Users WHERE username = '$user'";
    foreach ($db->query($sql) as $row) {
        $firstname.=$row['firstname'];
    }
    return $firstname;
}

Answer 2

使用这个

function getFirstname($db) {
    global $user;
    $firstname=false;
    $sql = "SELECT firstname FROM Users WHERE username = '$user'";
    foreach ($db->query($sql) as $row) {
        $firstname .= $row['firstname'];
    }
    return $firstname;
}

Answer 3

尝尝这个

<?php $user = $_SESSION["UserID"];?>
<?php
$user = $_SESSION["UserID"]; 

function getFirstname($db) {
    $firstname=false;
    global $user;
    $sql = "SELECT `firstname` FROM `Users` WHERE `username` = '{$user}'";
    foreach ($db->query($sql) as $row) {
        $firstname=$row['firstname'];
    }
    return $firstname;
}

$firstname=getFirstname( $db );
?>

<?php echo $firstname  ?>