How to remove excess whitespaces from a string?

I was looking for a small and quick way to remove excess whitespaces from a string. Sometimes you get SQL statement (or any other string) with whitespaces and need to clean it before your function starts to work with it.

For example:

$sql = "SELECT 
          id, field1, field2 ....
        FROM table
        WHERE status = 1";

And after trying some ways we found, that using preg_replace() function is the best one.

Here the pimpliest way how to do this:

$sql = preg_replace('/\s\s+/', ' ', $sql);