在表PHP中查找空值

Question

这是用于检查行中username = something

的值的代码

$stmt1 = $conn->prepare("SELECT likedOne FROM UserData WHERE username = ?");
$stmt1->bind_param('s',$username);
//$username = $_POST["username"];
$username ="jim";
$stmt1->execute();
$stmt1->store_result();

此法规会检查Value是否为空？

if ($stmt1 == ''){}

它不能正常工作。

Answer 1

试试这个

$stmt1->num_rows > 0

或

$res = $stmt1->fetch();

if( !empty( $res )
{

}

现在您的代码看起来像

$stmt1 = $conn->prepare("SELECT likedOne FROM UserData WHERE username = ?");
$username ="jim";
$stmt1->bind_param('s', $username);
$stmt1->execute();
$stmt1->store_result();

if($stmt1->num_rows > 0)
{
    //data retrive condition here
}

Answer 2

您可以通过多种方式查看，

if ($stmt1 === null){ } // This checks if the variable, by type, IS null.

OR

if (empty($stmt1)){ }

OR

if (!isset($stmt1)){ }

!isset($stmt1)检查变量是否未定义，如果变量是空的，则不会。