How to retrieve data using select box with PHP? - php

Question

I have more than 100 rows in an database and they are from different subjects, like Database lessons or Network lessons. I want that the user can choose what questions from those subjects he want to display. So I was thinking in using one select box, but I don't know how to handle the selected box with the database query. How could I do that ?
My code currently :
<div class = "container-fluid">
<div class = "container">
<?php
$query = "SELECT def_conteudo FROM conteudo WHERE nro_conteudo BETWEEN 1 AND 100";
$result = mysqli_query($con,$query);
while($fetch = mysqli_fetch_row($result)){
echo "<li>" . $fetch[0] . "</li>";
}
?>
</div>
</div>
The problem is that he just shows all the lessons from different subjects here, but I want to give the user the choice to choose what questions he want to display.
Example :
If the user want to display only Database lessons he would choose through the select box and would appear at the screen all questions from this particular subject, not all the subjects questions.

Answer 1

The HTML <select> element takes a list of <option> elements:
<select>
<option value="1">Option 1</option>
<option value="2">Option 2</option>
</select>
That snippet will produce a drop-down list to pick from the options Option 1 and Option 2 whose values are 1 and 2 respectively: https://jsfiddle.net/ux245gz3/
For your case, every <li> element you're creating should be an <option> inside of a <select> block:
<div class="container-fluid">
<div class="container">
<select id="subject_selection">
<?php
$query = "SELECT def_conteudo FROM conteudo WHERE nro_conteudo BETWEEN 1 AND 100";
$result = mysqli_query($con,$query);
while($fetch = mysqli_fetch_row($result)){
echo "<option value=\"$fetch[0]\">" . $fetch[0] . "</option>";
}
?>
</select>
</div>
</div>
This will produce a list of each of the names of the subjects with the value of the selection set to the displayed name. The MDN article on <select> will have more information about this.
Update to answer the full question:
You'll want to update the query to select a display value and the ID for each subject (assuming the primary key of the 'conteudo' table is called 'id':
SELECT id, def_conteudo FROM conteudo WHERE nro_conteudo BETWEEN 1 AND 100;
Then you can use the id as the value for each option:
<?php
$query = "SELECT id, def_conteudo FROM conteudo WHERE nro_conteudo BETWEEN 1 AND 100";
$result = mysqli_query($con, $query);
while ($fetch = mysqli_fetch_row($result)) {
echo "<option value=\"$fetch[0]\">$fetch[1]</option>";
}
?>
Then, once the user selects an option from the dropdown you can perform a GET to the page and query against the questions or lessons that have the proper relationship to the selected subject via the subject's id submitted by the form.
SELECT * FROM <licao/pergunta> WHERE contuedo_id = $_GET["id"];
As a friendly aside, at this point you should look into using something like PHP's PDO library to automatically handle sanitizing your dynamically generated SQL statements.