```ruby= gsub vs gsub! 3.*2 + 1 # ==> 7 3.*(2 + 1) # ==> 9 array.map(&:method_name) array.map {|a| a.method_name } :method_name.to_proc includes Foo extends Foo find find_by where each find_each includes joins - preload vs eager_load HAVING CURSOR EXPLAIN ANALYZE SEQUENCE VACUUM CTE ```