MySQL查询可在工作台中运行，但无法通过PHP接口运行

Question

I have a MySQL query that I know to be working in Workbench/Sequel Pro that appears to return empty in my PHP code:

$SQL = "SELECT * FROM staff, invigilation, exam, occupation, room, module
            WHERE staffID='$inputID'
            AND invigilation.examID=exam.exam_ID
            AND exam.exam_ID=occupation.examID
            AND room.room_ID=occupation.roomID
            AND exam.module_ID=module.module_ID
            AND staff.password='$inputPassword'";
            $result = mysql_query($SQL);

            if($db_field = mysql_fetch_assoc($result)) {

            echo "
            <table border='1'>
                <tr>
                    <th>Exam ID</th>
                    <th>Module ID</th>
                    <th>Module name</th>
                    <th>Duration</th>
                    <th>Start time</th>
                    <th>Room</th>
                </tr>";



                while ($db_field = mysql_fetch_assoc($result)) {
                echo "
                <tr>
                    ";
                    echo "<td>" . $db_field['exam_ID'] . "</td>";
                    echo "<td>" . $db_field['module_ID'] . "</td>";
                    echo "<td>" . $db_field['module_name'] . "</td>";
                    echo "<td>" . $db_field['duration'] . "</td>";
                    echo "<td>" . $db_field['start_datetime'] . "</td>";
                    echo "<td>" . $db_field['room_name'] . "</td>";

                    echo "
                </tr>";
                } 

            } else {
                    echo "Incorrect login details. Please try again";
                    die();
                }

The result of this code is the first table row (Exam ID, Module ID etc.) is displayed but the table content is not.

I cannot work out why this is happening. Other than the SQL query, the code is identical to code used elsewhere (where it is working fine).

Answer 1

You are doing mysql_fetch_assoc twice . The first time it reads the record and prints the table header. The second time there are no more records so it doesn't print a row.

Change

if($db_field = mysql_fetch_assoc($result)) {

to

if(mysql_num_rows($result) > 0) {

Answer 2

Try this. You are using mysql_fetch_assoc($result); two times, First time it get result and second time there is no result.

 $SQL = "SELECT * FROM staff, invigilation, exam, occupation, room, module
                WHERE staffID='$inputID'
                AND invigilation.examID=exam.exam_ID
                AND exam.exam_ID=occupation.examID
                AND room.room_ID=occupation.roomID
                AND exam.module_ID=module.module_ID
                AND staff.password='$inputPassword'";
                $result = mysql_query($SQL);
    $db_field = mysql_fetch_assoc($result)
                if($db_field != "" ) {

                echo "
                <table border='1'>
                    <tr>
                        <th>Exam ID</th>
                        <th>Module ID</th>
                        <th>Module name</th>
                        <th>Duration</th>
                        <th>Start time</th>
                        <th>Room</th>
                    </tr>";



                    while ($db_field) {
                    echo "
                    <tr>
                        ";
                        echo "<td>" . $db_field['exam_ID'] . "</td>";
                        echo "<td>" . $db_field['module_ID'] . "</td>";
                        echo "<td>" . $db_field['module_name'] . "</td>";
                        echo "<td>" . $db_field['duration'] . "</td>";
                        echo "<td>" . $db_field['start_datetime'] . "</td>";
                        echo "<td>" . $db_field['room_name'] . "</td>";

                        echo "
                    </tr>";
                    } 

                } else {
                        echo "Incorrect login details. Please try again";
                        die();
                    }