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Let's talk about the indexing principle of mysql. The secret of the text is that it is close to the topic. So, no gossip, let's go straight to the following, I believe you will benefit from reading this article on the indexing principles of mysql.

The purpose of the index

The purpose of indexing is to improve query efficiency, which can be compared to dictionaries. If we want to look up the word "mysql", we definitely need to locate the m letter, then find the y letter from the bottom down, and find the rest of the sql. If there is no index, then you may need to look through all the words to find what you want. What if I want to find the word that starts with m? Or what about the words that begin with ze? Do you think this can't be done without an index?

Principle of mysql indexing

In addition to dictionaries, examples of indexes can be found everywhere in life, such as the train schedule of the railway station, the catalogue of books, and so on. Their principle is the same, by constantly narrowing the scope of the data we want to filter out the final results, while turning random events into sequential events, that is, we always lock the data in the same way.

The same is true of the database, but it is obviously much more complex, because it faces not only equivalence queries, but also scope queries (>,

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