Shulou(Shulou.com)05/31 Report--

This article mainly explains "what are the knowledge points related to InnoDB". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let Xiaobian take you to learn "What are the knowledge points about InnoDB?"

I. About count(*)

Knowledge point: MyISAM will directly store the total number, InnoDB will not, you need to scan by line.

The subtext is, for select count(*) from t; MyISAM returns instantaneously if the data is large, while InnoDB scans line by line.

Practice: For tables with a large amount of data, InnoDB should not easily select count(*), which consumes a lot of performance.

Common pit: MyISAM will return the result directly only when querying the total number of rows in the whole table. When the where condition is added, the two storage engines handle it similarly.

t_user(uid, uname, age, sex);

uid PK

age index

select count(*) where age

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