先放在这里，等有时间整理成文章
Task・・・you will only see the standard fields present on task object.
Event・・・you will only see the standard fields present on event object.
Activity(没有这个表)・・・从这里给task和event创建共用的自定义项目
Open Activities
OpenActivity・・・①Todo 关闭前到这里 ②Event过期前放在这里
Activity History
ActivityHistory ①Todo 关闭后到这里 ②Event过期后放在这里 ③活动录入的数据直接存在这里
SELECT subject FROM task
Select Name, (Select Subject from OpenActivities) from Opportunity__c
Select Name, (Select Subject from ActivityHistories) from Opportunity__c