This is personal study note Copyright and original reference are from: https://www.youtube.com/watch?v=J5b38kTWFNU&list=PLuHgQVnccGMDF6rHsY9qMuJMd295Yk4sa ================================================================================ - Consider the relationship between "Author" and "Text" Author id name 1 kim 2 park 3 lee Text id text 1 The journey of life 2 The beatiful sea 3 Let it go 4 What's your favorite movie Author_Text id author_id text_id 1 1 1 2 1 2 3 3 1 4 3 2 5 3 3 6 3 4 author () : text (N) author () : text (optional) ================================================================================ author (M) : text (N) author (mandatory) : text (optional) ================================================================================ - Consider the relationship between "Text" and "Reply" - Cardinality "One text" can have "multiple replies" "One reply" can have "one text" - Optionality "One text" can have "no reply" "One reply" must have "text" - Table scheme Text id text 1 The journey of life 2 The beatiful sea 3 Let it go 4 What's your favorite movie Reply id content text_id 1 hi 1 2 good 1 3 bad 3 4 curious 3 5 sad 4 6 awesome 4 7 amazing 4 ================================================================================ text () : reply (N) text () : reply (optional) ================================================================================ text (1) : reply (N) text (mandatory) : reply (optional) ================================================================================ - Consider the relationship between "Author" and "Reply" - Cardinality "One author" can have "multiple replies" (N) "One reply" can have "one author" (1) - Optionality "One author" can have "no reply" (optional) "One reply" must have "author" (mandatory) - Table scheme Author id text 1 kim 2 park 3 lee Reply id content text_id 1 hi 1 2 good 1 3 bad 1 4 curious 3 5 sad 3 6 awesome 3 7 amazing 3 ================================================================================ reply : author (1) reply : author (mandatory) ================================================================================ reply (N) : author (1) reply (optional) : author (mandatory)