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select_type | table | type  | possible_keys                    | key              | key_len | ref                     | rows   | Extra                                        |
------------+-------+-------+----------------------------------+------------------+---------+-------------------------+--------+----------------------------------------------+
SIMPLE      | t1    | range | customer_number,transaction_date | transaction_date |       3 | NULL                    | 266699 | Using where; Using temporary; Using filesort |
SIMPLE      | t2    | ref   | customer_number,transaction_date | customer_number  |       8 | chai.t1.customer_number |      3 | Using where                                  |