How to use the `column_count` method of Statement?

[gmosx]

I am wondering, how is the column_count method supposed to be used.

AFAICU, you have to prepare and execute (query) the Statement, before you can call this method:

let mut stmt = conn.prepare(sql)?;
let mut rows = stmt.query([])?;
let column_count = stmt.column_count();

// IMPORTANT:
while let Some(row) = rows.next().unwrap() {
    ...
}

The problem is that the query* methods take a mutable reference to the Statement. When trying to call the column_count method, the borrow-checker complains:

cannot borrow `stmt` as immutable because it is also borrowed as mutable

Please note that the error is only triggered if the rows variable is actually used!

I would like to use the column count when 'deserializing' the rows. Any help/hints will be appreciated.