多表关联时因为字符集不一致导致索引失效

SELECT t1.*FROM t1 LEFT JOIN t2 ON t2.capital_unique_code = t1.unique_codeWHERE t1.trade_date >= '2020-12-24' AND t1.trade_date <= '2020-12-24' AND t1.capital_account IN ('95200078801700000859', 'dev@souche.com', 'sousou@souche.com')ORDER BY t1.trade_date, t1.trade_time, t1.idLIMIT 50 图上sql  t1. unique_code utf8mb4 字符集t2. capital_unique_code是utf8支付集 因为字符集不一致 导致了索引失效 +----+-------------+-------+------------+-------+--------------------------------+--------------------------------+---------+------+---------+----------+-----------------------------------------------------------------+| id | select_type | table | partitions | type  | possible_keys                  | key                            | key_len | ref  | rows    | filtered | Extra                                                           |+----+-------------+-------+------------+-------+--------------------------------+--------------------------------+---------+------+---------+----------+-----------------------------------------------------------------+|  1 | SIMPLE      | t1    | NULL       | range | idx_trade_date_capital_account | idx_trade_date_capital_account | 257     | NULL |      34 |   100.00 | Using index condition; Using temporary; Using filesort          ||  1 | SIMPLE      | t2    | NULL       | index | NULL                           | uniq_key                       | 303     | NULL | 2348088 |   100.00 | Using where; Using index; Using join buffer (Block Nested Loop) |+----+-------------+-------+------------+-------+--------------------------------+--------------------------------+---------+------+---------+----------+-----------------------------------------------------------------+ 修改字符集为一致之后 +----+-------------+-------+------------+-------+--------------------------------+--------------------------------+---------+---------------------------+------+----------+---------------------------------------+| id | select_type | table | partitions | type  | possible_keys                  | key                            | key_len | ref                       | rows | filtered | Extra                                 |+----+-------------+-------+------------+-------+--------------------------------+--------------------------------+---------+---------------------------+------+----------+---------------------------------------+|  1 | SIMPLE      | t1    | NULL       | range | idx_trade_date_capital_account | idx_trade_date_capital_account | 257     | NULL                      |   34 |   100.00 | Using index condition; Using filesort ||  1 | SIMPLE      | t2    | NULL       | ref   | uniq_key                       | uniq_key                       | 403     | sfs_server.t1.unique_code |    1 |   100.00 | Using where; Using index              |+----+-------------+-------+------------+-------+--------------------------------+--------------------------------+---------+---------------------------+------+----------+---------------------------------------+