需求：获取指定用户下某个邮箱最近一次发送时间
场景：
CREATE_TIME已经添加索引
原语句：(max导致全表扫描！！！)
SELECT MAX(CREATE_TIME) AS MAX0 FROM t_mail_send_extend WHERE USER_ID = ‘03515d6956c0434c86175835b9fae0bf‘ AND LOCATE( ‘sebastian.sandoli@ladespensa.es‘, ADDRESS ) AND STATUS = 1
改进：
SELECT CREATE_TIME FROM t_mail_send_extend WHERE USER_ID = ‘03515d6956c0434c86175835b9fae0bf‘ AND LOCATE( ‘sebastian.sandoli@ladespensa.es‘, ADDRESS ) AND STATUS = 1 ORDER BY CREATE_TIME DESC LIMIT 1
原文：https://www.cnblogs.com/wanhua-wu/p/12917154.html