准备好的语句未在 PHP 中执行，但在 SQL 控制台上完美运行

Question

function examResult($student_id, $exam_id){
        global $conn;
        
        $stmt = $conn->prepare("SELECT SUM(CASE WHEN answers.answered_option=questions.correct_option THEN questions.marks ELSE 0 END) AS obtain, exams.exam_name, exams.total_marks, exams.pass_marks FROM exams INNER JOIN questions ON exams.id=questions.exam_id INNER JOIN answers ON answers.question_id=questions.id WHERE answers.student_id = ? AND exams.id = ? ");
        
        
        if($stmt){
            return 'ok';
            $stmt->bind_param('ii', $student_id, $exam_id);
            $stmt->execute();
            $result = $stmt->get_result();
            if($result){
                $row = $result->fetch_assoc();
                return $row;
            }
        } else{
            return false;
        }

    }

I was expecting 'ok' from the above function but it returning false. That means the $stmt is not executing. Also my both parameters $student_id & $exam_id are fine.

But if I execute it in my SQL console like below it works perfectly.

SELECT SUM(CASE WHEN answers.answered_option=questions.correct_option THEN questions.marks ELSE 0 END) AS obtain, exams.exam_name, exams.total_marks, exams.pass_marks FROM exams INNER JOIN questions ON exams.id=questions.exam_id INNER JOIN answers ON answers.question_id=questions.id WHERE answers.student_id = 18 AND exams.id = 24

Answer 1

function examResult($student_id, $exam_id){
        global $conn;
        
        $stmt = $conn->prepare("SELECT SUM(CASE WHEN answers.answered_option=questions.correct_option THEN questions.marks ELSE 0 END) AS obtain, exams.exam_name, exams.total_marks, exams.pass_marks FROM exams INNER JOIN questions ON exams.id=questions.exam_id INNER JOIN answers ON answers.question_id=questions.id WHERE answers.student_id = ? AND exams.id = ? ");
        
        
        if($stmt){
            return 'ok';
            $stmt->bind_param('ii', $student_id, $exam_id);
            $stmt->execute();
            $result = $stmt->get_result();
            if($result){
                $row = $result->fetch_assoc();
                return $row;
            }
        } else{
            return false;
        }

    }

I was expecting 'ok' from the above function but it returning false. That means the $stmt is not executing. Also my both parameters $student_id & $exam_id are fine.

But if I execute it in my SQL console like below it works perfectly.

SELECT SUM(CASE WHEN answers.answered_option=questions.correct_option THEN questions.marks ELSE 0 END) AS obtain, exams.exam_name, exams.total_marks, exams.pass_marks FROM exams INNER JOIN questions ON exams.id=questions.exam_id INNER JOIN answers ON answers.question_id=questions.id WHERE answers.student_id = 18 AND exams.id = 24