MySQL -- index principle + how to use

One 、 Introduce

Why an index ?

　　 General application system , The proportion of reading and writing is 10:1 about , And insert operations and general update operations rarely have performance problems , In the production environment , We met the most , It's also the most problematic , Or some complex query operations , Therefore, the optimization of query statements is obviously the top priority . Speaking of accelerating query , I have to mention index .

What is index ？

　　 Index in MySQL Also known as “ key ”, It is a data structure used by the storage engine to quickly find records . Indexing for good performance
It's critical , Especially when there is more and more data in the table , The impact of indexes on performance is increasingly important .
Index optimization should be the most effective way to optimize query performance . Indexes can easily improve query performance by several orders of magnitude .
Index the phonetic order of a dictionary , If you want to find a word , If you don't use a sound sequence table , It needs to be checked page by page from hundreds of pages .

Do you have any misunderstanding about index ？

Indexing is an important aspect of application design and development . If there are too many indexes , The performance of the application may be affected . There are too few indexes , It also has an impact on query performance , To find a balance , This is critical to the performance of the application . Some developers always think of adding indexes after the fact ---- I always thought , It comes from a wrong development model . If you know the use of data , You should add indexes where you need them from the beginning . Developers often use the database at the application level , For example, writing SQL sentence 、 Stored procedures and so on , They may not even know the index exists , Or think it's relevant after the event DBA Add it on .DBA Often not enough to understand the data flow of the business , Adding indexes requires monitoring a large number of SQL The sentence then finds the problem , The time required for this step must be much longer than the time required for the initial index addition , And may miss a part of the index . Of course, there are not many indexes