Can you retrieve a list of updated rows when running an UPDATE query using the Go sqlx package with Postgres?

I have a query I'm running using Go's sqlx package (an extension to the standard database/sql package) with a Postgres database. It looks something like this:

result, err := s.getDB(tx).Exec(`
    UPDATE table_name
    SET var_name = 0
    WHERE var_name = 1;`)
if err != nil {
    return nil, err
}

Without using a managed transaction, how can I retrieve the list of updated rows? Or at least a list of primary keys for the updated rows?