# File lib/sqlite_magic.rb, line 20
    def add_columns(tbl_name, col_names)
      existing_cols = database.table_info(tbl_name).map{ |c| c['name'] }
      missing_cols = col_names.map(&:to_s) - existing_cols
      missing_cols.each do |col_name|
        database.execute("ALTER TABLE #{tbl_name} ADD COLUMN #{col_name}")
      end
    end