Sub-optimal count query for topicMapper.selectAll

[wtune]

For finding topics with user information via the automatic paged query selectAll, a query counting the total number of rows selectAll retrieves will be issued:

SELECT 
  COUNT(1) 
FROM 
  (
    select 
      t.*, 
      u.username, 
      u.avatar 
    from 
      topic t 
      left join user u on t.user_id = u.id 
    order by 
      t.top desc, 
      t.in_time desc
  ) TOTAL

However, since the query use topic to left join user table on primary key u.id, the final result is the same to query select count(1) from topic without any join operator or order by. So the counting query has a chance to be optimized.

[atjiu]

select count (1) This query is done by mybatis-plus framework, I did not write this sql