MySQL format 字符集問題

Oracle遷移mysql修改語法時，發現日期比較出現報錯，原因是date_format函數返回字符集

1. 報錯片段，其中BEGIN_DATE是data_time類型

SELECT * FROM xxx a where date_format('2018/11/1', '%Y-%m') < a.BEGIN_DATE;

1. 官方解釋

DATE_FORMAT() returns a string with a character set and collation given by character_set_connection and collation_connection so that it can return month and weekday names containing non-ASCII characters.

1. 直接說方案吧
   方案一：兩邊都date_format

  SELECT * FROM xxx a where date_format('2018/11/1', '%Y-%m') < date_format(a.BEGIN_DATE, '%Y-%m-%d');  

方案二：前面的常量format字符串加上“日”，’%Y-%m-%d’

SELECT * FROM xxx a where date_format('2018/11/1', '%Y-%m-%d') < a.BEGIN_DATE;

方案三：表字段放在前面

SELECT * FROM xxx a where a.BEGIN_DATE > date_format('2018/11/1', '%Y-%m') ;