select t.task_id,t.task_name,table1.log_count
from task_info t
LEFT JOIN (select task_id,count(task_id) log_count from log_info GROUP BY task_id) as table1
on t.task_id=table1.task_id
一个任务task_info对应多个日志log_info,一个日志log_info对应一个任务task_info
select t.task_id,t.task_name,table1.log_count
from task_info t
LEFT JOIN (select task_id,count(task_id) log_count from log_info GROUP BY task_id) as table1
on t.task_id=table1.task_id
一个任务task_info对应多个日志log_info,一个日志log_info对应一个任务task_info