How do ORDER BY with information that may vary?

Question

I’m getting a list of articles from a database and I want to have on page one tool that allows me to list them in order of date they were written or in alphabetical order.

Here I have my bank reading function:

$sel = DBRead('artigos', null ,'*', 'ORDER BY data ASC');

If I let data the listing is made starting with the oldest post, if I change to nome the listing is done in alphabetical order.

I built a form in HTML with a "select" and two "options" inside and through the POST method I can get the value of one of these "option’s" and put in the variable $mudanca.

But if I put the variable in the reading function gives error:

$sel = DBRead('artigos', null ,'*', 'ORDER BY $mudanca ASC');

Any different suggestions?

I add something that might be useful to someone who’s building the same thing:

 <?php 
  $mudanca="data";
 if ($_SERVER["REQUEST_METHOD"] == "POST"){
 $mudanca = $_POST['mudar'];
 }   
 ?>

That is, leave a default variable set, because before the post method is triggered $change would be empty causing error in ORDER BY $mudanca.

Answer 1

Put it like this:

$sel = DBRead('artigos', null ,'*', "ORDER BY $mudanca ASC");

I mean, double quotes!

Inside single quotes PHP does not interpret anything it puts what is in it as a text only, while in double quotes if you have PHP variables for example it will interpret and show you the result.

$texto = 'imprime texto';
echo '$texto'; // saída -> $texto
echo "$texto"; // saída -> imprime texto

Online Example: Ideone

Or

Concatenation

$sel = DBRead('artigos', null ,'*', 'ORDER BY '.$mudanca.' ASC');

Good reading.