mysql 更新 datetime 字段

语法：

update yourTableName
set yourDateTimeColumnName=yourDateTimeColumnName - interval yourValue day
where date(yourDateTimeColumnName)=’yourDateValue’;

样例：

update juanzeng set juanzeng_shijian = juanzeng_shijian + interval 12 day where date(juanzeng_shijian) = '2017-07-01' and xiangmu_id = 4;