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When to use NoSQL instead of RDBMS?

I've heard that if you have many "join"s in your RDBMS, that makes your service/app work slower. And also, in case of RDBMS you have to define the strict schema for your tables. I can't understand what are the pros and cons of NoSQL, can you bring a real-life example where NoSQL solves a real problem?

4/20/2018 9:21:13 AM


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-------(2)------- NoSQL: User {id: u1, uname: Burey} {id: u2, uname: vardanator} {id: u3, uname: Gandalf} {id: u4, uname: Papa Smurf} {id: u5, uname: Kramer} Post {id: p1, uid: u1, title: "Hello SL!", body: "How is.....", comments: [c1], likes: [l1, l2]} Comment {id: c1, uid: u2, body: "doing fine :]", likes: [l3, l4, l5, l6]} Like {id: l1, uid: u3} {id: l2, uid: u4} {id: l3, uid: u3} {id: l4, uid: u4} {id: l5, uid: u1} {id: l6, uid: u5} now this looks rather complex, but can be simplified: you can for example skip the Like schema and just keep a list of user ids in the posts and likes the usage with an actual collection schema can allow us to add additional fields more easily (timestamps for example) and a last word regarding the lists (posts, comments, likes): in the actual database they can be saves as references to the actual object, that's why i used names like c1, l1, l2, ...... various engines allow you to populate the actual object by the reference when querying the DB. for more info you can check these: https://www.sololearn.com/discuss/1156702/?ref=app https://www.sololearn.com/discuss/753417/?ref=app


-------(1)------- think of a message board with users, posts, comments to posts, and likes for the posts and comments to describe this in a relational database, a possible solution would need the following tables: id: row id uid: user id pid: post id cid: comment id body: just plain text of post/comment USERS(id, uname) POSTS(id, uid, title, body) COMMENTS(id, uid, pid, body) POSTS_LIKES(id, uid, pid) COMMENTS_LIKES(id, uid, cid) these tables could give you the ability to keep track of posts, comments, who liked what and so on. * it would be possible to merge the POSTS_LIKES and COMMENTS_LIKES to one table like so: LIKES(id, uid, pid, cid) and determine the relation by pid (post id) or cid (comment id) * we'll define possible schemas for the following collections: User, Post, Comment, Like * keep in mind that every object is generated with a unique id throughtout the entire DB, that's why i ommit "id" field from each schema * User(uname) Post(uid, title, body, comments, likes) Comment(uid , body, likes) Like(uid) one of the nice features of NoSQL is that it's actually structured as a document (in mongodb it's BSON format, which ia very similar to JSON). this allows to have lists as fields so the following post in SQL and NoSQL: Burey: Hello SL! ~~~~~~~~~~~~~~~~ How is evreyone doing? likes: 2 comments: vardanator: doing fine :] likes: 4 SQL: USERS id uname 1 Burey 2 vardanator 3 Gandalf 4 Papa Smurf 5 Kramer POSTS id uid title body 1 1 Hello SL! How is..... COMMENTS id uid pid body 1 2 1 doing fine :] LIKES id uid pid cid 1 3 1 NULL 2 3 NULL 1 3 4 1 NULL 4 4 NULL 1 5 1 NULL 1 6 5 NULL 1


-------(3)------- my fingers hurt now ._.