SQL study notes 06 Geek time SQL must know must speak 50

Thanks https://time.geekbang.org/column/article/118746

20 丨 When we think about database tuning, what dimensions are available?

21 丨 Paradigm design: What are the paradigms of the data table, and what does 3NF refer to?

22 丨 Anti-paradigm design: What are the disadvantages of 3NF, why is anti-paradigm design sometimes needed?

23 丨 Overview of indexing: whether to use index or not, this is a problem

24 丨 The principle of indexing: Why do we use B + tree for indexing?

25 丨 What is the underlying principle of Hash index?

26 丨 The principle of using index: How to maximize the efficiency of SQL query through index?

27 丨 Understanding B + tree query from the perspective of data pages

28 丨 Understand the cost of SQL queries from the perspective of disk I / O

29 丨 Why is there no ideal index?