请帮我优化如下mysql语句，SELECT aul_id, aul_fu_id, aul_fu_name, aul_fu_phone, aul_ac_name, aul_ac_id, aul_total_score, aul_end_time, aul_ss_id, aul_ip, aul_result, aul_start_time, aul_right_num, aul_err_num, aul_total_time, aul_al_score, aul_source, aul_relation, aul_name, aul_school, aul_class FROM answer_user_log WHERE ( aul_ac_id = '1575279135006396418' AND aul_fu_id = 1660208621145034754 AND aul_ss_id = 0 AND aul_source = 0 ) ORDER BY aul_end_time DESC LIMIT 1

可以考虑如下优化：

1. 添加合适的索引：可以为 `aul_ac_id`、`aul_fu_id`、`aul_ss_id`、`aul_source` 和 `aul_end_time` 字段各添加一个索引。

2. 只选择需要的列：可以只选择需要的列，而不是选择所有列。这可以通过指定列名来实现，如 `SELECT aul_id, aul_fu_id, aul_fu_name, ...`。

3. 使用 EXISTS 替代 LIMIT：可以使用 EXISTS 替代 LIMIT 语句，如下所示：

   SELECT aul_id, aul_fu_id, aul_fu_name, ...
   FROM answer_user_log aul
   WHERE aul_ac_id = '1575279135006396418'
     AND aul_fu_id = 1660208621145034754
     AND aul_ss_id = 0
     AND aul_source = 0
     AND NOT EXISTS (
       SELECT 1
       FROM answer_user_log aul2
       WHERE aul2.aul_ac_id = aul.aul_ac_id
         AND aul2.aul_fu_id = aul.aul_fu_id
         AND aul2.aul_ss_id = aul.aul_ss_id
         AND aul2.aul_source = aul.aul_source
         AND aul2.aul_end_time > aul.aul_end_time
     )
   ORDER BY aul_end_time DESC;

这样可以避免使用 LIMIT，从而提高查询效率。