How to explain the difference between SQL and NoSQL to little sister

　　Recently, there has been a problem in an interview on Medium: How to explain the difference between SQL and NoSQL to the grandmother. I think the authors use their own family tree structured to compare the differences between sql and nosql. Writing is very good, but a little awkward. The interviewer did not have time to listen to your words. Personally, I think the difference between sql and nosql disappeared. One or two sentences can not generalize, let alone tell grandma, so if you really asked this question, you can choose one of the main differences. This analogy is good. For example, sql is generic, and is a special nosql. So my answer is this:
　　My dear grandmother, the database is used to store data warehouses, container storage project as we used to live in the same, but these containers are also common and special. For example, generic container is a plastic bag, a plastic bag can accommodate a variety of things as: i.e. sweets or pencil can be accommodated. But we can also choose a more suitable storage: candy and candy. Candy box and pen holder are special containers. And the data items may be stored in a general or specific manner, have advantages and disadvantages. SQL is a conventional database, NoSQL is a special database. This is the difference between the two.
　　Set theory and relational algebra
　　but why SQL is generic? Tens of millions of data structures in the world. Why SQL and meet the various needs half a century are not out of date?
　　Although only constant is change, but the computer industry has been fission, but some basic things are the same, or change very slowly: JavaScript is the world's most popular programming language, Lisp language still insist on using 60 years ago. Standard modern operating systems Windows, OSX and Linux from a common ancestor Unix.
　　Development of the database are the same. Regardless of variations, set theory and its essence is about the design of the relational algebra. The basic theory of everything. As long as you have mastered the basic mathematical theory of the software industry, you can have all the laws change. This is SQL eternal secret. Source: Neural Networks