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  1. select some_other_column
  2. from `table`
  3. order by primary_index_column asc
  4. limit 4000000, 10;
  5.    
  6. select some_other_column
  7. from `table`
  8. order by secondary_index_column asc
  9. limit 4000000, 10;
  10.    
  11. mysql> explain select some_other_column from `table` order by primary_index_column limit 4000000, 10;
  12. +----+-------------+---------+-------+---------------+---------+---------+------+---------+-------+
  13. | id | select_type | table   | type  | possible_keys | key     | key_len | ref  | rows    | Extra |
  14. +----+-------------+---------+-------+---------------+---------+---------+------+---------+-------+
  15. |  1 | SIMPLE      | table   | index | NULL          | PRIMARY | 4       | NULL | 4000010 |       |
  16. +----+-------------+---------+-------+---------------+---------+---------+------+---------+-------+
  17.  
  18. mysql> explain select some_other_column from `table` order by secondary_index_column limit 4000000, 10;
  19. +----+-------------+---------+------+---------------+------+---------+------+---------+----------------+
  20. | id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra          |
  21. +----+-------------+---------+------+---------------+------+---------+------+---------+----------------+
  22. |  1 | SIMPLE      | table   | ALL  | NULL          | NULL | NULL    | NULL | 4642945 | Using filesort |
  23. +----+-------------+---------+------+---------------+------+---------+------+---------+----------------+
  24.    
  25. ALTER TABLE `table` ADD INDEX mynewndx (indexed_column,some_other_column);
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