mysql Update Statement depending on number of checkbox checked - php

Question

Problem statement:
I have a form with multiple checkbox Fields, i have validated it so
user can select maximum 9 checkbox and atleast 1 with jquery.
I collect the Form checked values using Post method.
i have mysql table with 12 columns.
first 3 columns are "id", "rollnum", "selectStatus"
Through session variables created during Login, i get roll number of student. So i can Run Update Query on particular row.
Question: How do i Update those 9 subject columns according to user checked inputs. Note : i stored those checked input field values in an array.
Code
<form action="index.php" id="form-3" method="post">
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="ucs303">UCS303 Operating Systems
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="ucs406">UCS406 Data Structures and Algorithms
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="uec401">UEC401 Analog Communication Systems
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="uec612">UEC612 Digital System Design
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="uec307">UEC307 Electromagnetic Field Theory & Trans Lines
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="uec502">UEC502 Digital Signal Processing
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="uec510">UEC510 Computer Architecture
<button type="submit" name="year-3-submit">Submit Selection</button>
</form>
<?php
if(isset($_POST['year-3-submit'])){
if(!empty($_POST['year-3-checkbox'])){
$subjectCheckList = array();
$subjectCheckList = $_POST['year-3-checkbox'];
}
}
?>
It depends on user how many checkbox is selected.
I donot know how to write UPDATE sql query which updates values of number of columns == size of array.
for example:
User 1 has selected 3 checkbox and submitted form, we have array of size 3 and UPDATE 3 columns of table.
User 1 has selected 6 checkbox and submitted form, we have array of size 6 and UPDATE 6 columns of table.
I donot want to write 9 switch case statements for all possible sizes
of array. Any idea? please?

Answer 1

Based on OP's comments, you can make the code generic as follows:
// Check if atleast one subject has been selected
$selectedSubjects = array_filter($subjectCheckList);
// If no subject selected
if (empty($selectedSubjects)) {
$sql = "UPDATE subjectmaster
SET substatus = 0
WHERE rollno = '" . mysqli_real_escape_string($rollnumber) . "'";
} else {
// Initialize the sql string
$sql = "UPDATE subjectmaster
SET substatus = 1 ";
$i = 1;
foreach ($subjectCheckList as $subject) {
$sql .= ", sub" . $i . " = '" . mysqli_real_escape_string($subject) . "' ";
}
$sql .= " WHERE rollno = '" . mysqli_real_escape_string($rollnumber) . "'";
}
Also, note the use of mysqli_real_escape_string. It helps in preventing SQL injection. For better ways to prevent SQL injection, you may check How can I prevent SQL injection in PHP?

Answer 2

Well, 1st of all it is not clear what should be the default valued for each column.
Since your MySQL columns are set by numbers (sub1, sub2, etc) then your form should represent them accordingly, with the proper value. for example:
<input class="form-check-input" name="year-3-checkbox[]" type="checkbox" value="1">
This way, you can loop easily and update the table (I assume the sub columns are TINYINT(1) DEFAULT NULL) :
<?php
if(isset($_POST['year-3-submit'])){
if(!empty($_POST['year-3-checkbox'])){
$subjectCheckList = array();
$query = "UPDATE table SET ";
foreach ($_POST['year-3-checkbox'] as $key => $value) {
$query .= " sub" . $value . " = 1, "
}
$query = substr($query, 0, -1);
}
}
?>
Hope this helps
Guy

Answer 3

You can also use array_filter, array_combine and array_slice.
<?php
$subs = [':sub1',
':sub2',
':sub3',
':sub4',
':sub5',
':sub6',
':sub7',
':sub8',
':sub9'
];
// use $dataFromForm = array_filter($_POST['year-3-checkbox'])
$dataFromForm = ['11111',
'222222',
'3333333'];
$dbh = new PDO('mysql:host=localhost;dbname=test', 'root', '*******');
$sql = 'UPDATE test SET sub1 = :sub1, sub2 = :sub2, sub3 = :sub3, sub4 = :sub4, sub5 = :sub5, sub6 = :sub6, sub7 = :sub7, sub8 = :sub8, sub9 = :sub9';
$sth = $dbh->prepare($sql);
$sth->execute(array_combine(array_slice($subs, 0, count($dataFromForm), $dataFromForm)));