Question

我在下面有一个动态where子句的查询，但是我遇到了放置GROUP BY和ORDER BY子句的问题。我认为它根本没有被触发，因为准备声明超出了这些条款。但它不仅仅允许我将子句行放在准备语句之上，或者它给出了一个错误，在完全不同的行中陈述未定义的问题。我的问题是GROUP BY和ORDER BY CLAUSE应该在哪里正确放置？

CODE：

$selectedstudentanswerqry = "
        SELECT
        sa.StudentId, StudentAlias, StudentForename, StudentSurname, q.SessionId, 
    ...
        FROM Student st
    ...
        ";

        // Initially empty
            $where = array('q.SessionId = ?');
            $parameters = array($_POST["session"]);
            $parameterTypes = 'i';


        //check if POST is empty

        // Check whether a specific student was selected

        $p_student = empty($_POST["student"])?0:$_POST["student"];  // Now if $_POST['student'] is either 0 or empty $p_student will be 0
    echo $p_student;
        switch($p_student){
        case 0:
            //dont' add where filters
            break;
        default:
            $where[] = 'sa.StudentId = ?';
            $parameters[] .= $_POST["student"];
            $parameterTypes .= 'i';
        }


        // If we added to $where in any of the conditionals, we need a WHERE clause in
        // our query
        if(!empty($where)) {
            $selectedstudentanswerqry .= ' WHERE ' . implode(' AND ', $where);
            global $mysqli;
            $selectedstudentanswerstmt=$mysqli->prepare($selectedstudentanswerqry);
            // You only need to call bind_param once

            if (count($where) == 1) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0]);
        }
        else if (count($where) == 2) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0], $parameters[1]);
        }

        }

        $selectedstudentanswerqry .= "
          GROUP BY sa.StudentId, q.QuestionId
          ORDER BY StudentAlias, q.SessionId, QuestionNo
        ";

Answer 1

在GROUP BY / ORDER BY子句下移动包含bind_param（）的prepare语句和if语句。您在}之上的收盘$selectedstudentanswerqry可以上移到if (count($where) == 1)以上

准备声明（mysqli）之后的GROUP BY和ORDER BY子句

1 个答案: