Update in PDO/SQL with a variable number of variables :) - php

Question

I have a code that retrieves all the input data sent in a form. If the form had only 2 fields filled out, the PHP gets the value for only those 2 fields (the unchanged fields in the form are not submitted).
Then I would like to UPDATE a SQL table for those fields that I have retrieved with my PHP code. Here is where I am lost. I would need to specify in the SQL only the fields that I have received from the form, but this is variable. Maybe I received only 1 field, maybe I received 7 of the fields...
Here is my code:
if (isset($_POST) && !empty($_POST)) {
echo $internalImage;
foreach ($_POST as $key => $value)
{
echo "Field Name: ".htmlspecialchars($key)." | Value: ".htmlspecialchars($value)."<br>";
}
}
What would you suggest?

Answer 1

You could construct your query like this:
$values=array();
//this will be an array of possible fields that are in your table
$possible=array('field1', 'field2', 'field3');
$i=0;
$len=count($_POST);
$query='update table_name set ';
foreach($_POST as $key => $value){
$k=htmlspecialchars($key);
$v=htmlspecialchars($value);
if(in_array($k, $possible)){
$query .= $k .' = ?'; //placeholder for a value
$values[]=$v; //append values to an array for later use
if($i < ($len-1)) $query .= ', ';
$i++;
}
}
$query .= 'where table_id = ?';
$values[]=$table_id; //forgot that, append id of a row you are to update.
and then prepare and execute the query:
$db->prepare($query);
$db->execute($query, $values);