The explain plan

How MySQL executes queries is one of the major factors of database performance. You can verify the MySQL execution plan using the EXPLAIN command. Starting from MySQL 5.7.2, you can use EXPLAIN to examine queries currently executing in other sessions. EXPLAIN FORMAT=JSON gives detailed information.

How to do it...

Let's get into the details.

Using EXPLAIN

The explain plan gives information on how the optimizer is going to execute the query. You just need to prefix the EXPLAIN keyword to the query:

mysql> EXPLAIN SELECT dept_name FROM dept_emp JOIN employees ON dept_emp.emp_no=employees.emp_no JOIN departments ON departments.dept_no=dept_emp.dept_no WHERE employees.first_name='Aamer'\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: employees
   partitions: NULL
         type: ref
possible_keys: PRIMARY,name
          key: name
      key_len: 58
          ref: const
         rows: 228
     filtered: 100.00...