Records stored in mysql are generally not divided into fields and are stored as a whole.
Tools for optimizing SQL include: explain: used to analyze whether to apply indexes and the number of scanned records; slow log generally records SQL statements whose execution time is greater than a certain value; show profiles generally analyzes data on IO, Memory, CPU, etc.

Use execution plan, explain

Set in my.cnf

php[mysqld] 
slow_query_log=on 
slow_query_log_file=mysql-slow

Slow query log analysis tool officially provided by mysqlmysqldumpslow mysql-slow
Also mysqlsla

Use explain command

Must explain

It is recommended to use Alibaba's druid database connection pool. Configure it to record all SQL execution statistics for a period of time. There will be a web page that can be accessed, which is very helpful for SQL execution analysis. However, the cache of this thing takes up a lot of space, and it cannot count long-term running conditions. It is very suitable for analyzing the amount of data for several hours.