Use the mind mapping tool to use mysql to summarize the knowledge.
Focus on explaining
id SELECT identifier. This is the SELECT query sequence number. This is not important, the query sequence number is the order in which the SQL statement is executed
select_type select type
The table used by the rows output by table, this parameter is obvious and easy to understand
partitions
type connection type. There are multiple parameters, starting from the best type to the worst type is important and difficult
possible_keys hints which index to use will find rows in this table, not too important
The index used by keys MYSQL is simple and important
key_len The index length used by MYSQL
ref The ref column shows which column or constant is used with the key to select the row from the table.
rows shows the number of rows MYSQL executes the query, simple and important, the larger the value, the worse it is, indicating that the index is not used well
Extra This column contains details of how MySQL resolves the query.