如果用户选择“全部”，如何从所有选项中检索数据

Question

Got a mysqli/php code below where it will display results depending on option selected from the question drop down menu:

$selectedquestionqry = "
SELECT
QuestionNo
FROM
Question
WHERE
(QuestionId = ?)
";

global $mysqli;
$selectedquestionstmt=$mysqli->prepare($selectedquestionqry);
// You only need to call bind_param once
$selectedquestionstmt->bind_param("i",$_POST["question"]);
// get result and assign variables (prefix with db)
$selectedquestionstmt->execute(); 
$selectedquestionstmt->bind_result($selQuestionNo);
$selectedquestionstmt->store_result();
$selquestionnum = $selectedquestionstmt->num_rows();   


 while ($selectedquestionstmt->fetch()) {

if($_POST["question"] === '0') {
    echo "<p>All Questions - Total:(" . $selquestionnum . ")</p>" . PHP_EOL;
}else if($_POST["question"] !== '0') {
echo "<p><strong>Questions: </strong>" . $selQuestionNo . "</p>" . PHP_EOL;
}
}

DROP DOWN MENU:

 <select name="student" id="studentsDrop">
    <option value="0">All</option>
    <option value="23">Jay Hart</option>
    <option value="32">Bubba Wright</option>
    </select>

My question is that how can I get it so that if the user has selected '0', then it will be able to select all questions from the db which are displayed in the question drop down menu?

The reason I am asking this is because in my echo else if($_POST["question"] !== '0') { echo "<p><strong>Questions: </strong>" . $selQuestionNo . "</p>" . PHP_EOL; }, nothing is being echo when I select the All option, which to me makes me think that it is not displaying the echo due to this. If I select a single question from drop down menu, it is able to output it's echo.

Answer 1

you just need to modify your query:

if($_POST["question"] === '0') {
    $selectedquestionqry = "SELECT QuestionNo FROM Question";
} else {
    $selectedquestionqry = "SELECT QuestionNo FROM Question WHERE (QuestionId = ?)";
}