mysql中时间比较大小，字符串转date进行时间比较

https://blog.csdn.net/ljj125896/article/details/84034652?utm_medium=distribute.pc_aggpage_search_result.none-task-blog-2~all~first_rank_v2~rank_v28-1-84034652.nonecase&utm_term=varchar%E8%BD%AC%E6%8D%A2%E6%88%90date&spm=1000.2123.3001.4430

https://blog.csdn.net/liu865033503/article/details/81289259?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-2.channel_param&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-2.channel_param

-- VISIT_TIME 是varchar  VISIT_TIME_STRING 是datetime

SELECT id, VISIT_TIME, VISIT_TIME_STRING FROM MEM_VISIT_APPOINTMENT WHERE VISIT_TIME_STRING > NOW();

SELECT id, VISIT_TIME, VISIT_TIME_STRING FROM MEM_VISIT_APPOINTMENT WHERE  STR_TO_DATE(VISIT_TIME,'%Y-%m-%d %k:%i:%s' ) > NOW();

-- STR_TO_DATE('2012-8-8 14:58:09','%Y-%m-%d %k:%i:%s' ) A