Mysql: 21 best practices for performance optimization 2 [EXPLAIN your SELECT query]

EXPLAIN your SELECT query

The EXPLAIN keyword helps you know how MySQL processes your SQL statements. This helps you analyze the performance bottleneck of your query statement or table structure.
The EXPLAIN query results also show you how your index primary key is used and how your data tables are searched and sorted ...... And so on.
SELECT one of your SELECT statements (we recommend that you SELECT the most complex one with multi-table join) and add the keyword "EXPLAIN" to the front. You can use phpmyadmin to do this. Then, you will see a table. In the following example, we forget to add the group_id index and have table join:

After adding an index to the group_id field:

We can see that the previous result shows that 7883 rows are searched, and the last one only searches 9 and 16 rows of two tables. Viewing the rows column allows us to find potential performance problems.