This is personal study note Copyright and original reference: https://www.youtube.com/watch?v=f_KCIBfEhNY&list=PLuHgQVnccGMDF6rHsY9qMuJMd295Yk4sa ================================================================================ JOIN is computationally expensive task ================================================================================ After that, you want to get "tag name", and you need to use "join" ================================================================================ To remove "JOIN", tag name is inserted into topic_tag_relation table Even if that table has duplicate, you can remove "join" for above task ================================================================================ ================================================================================ Denormalization causes "higher complicated program", "easy break down"