Differences between MySQL Union and union all

union: For multiple result sets (select sentence ) To perform union operations , Do not include repeating lines , Sort at the same time .

union all: For multiple result sets (select sentence ) To perform union operations , Include repeating lines , No sorting .

Inside select Statements must have the same number of columns , Columns must also have similar data types , At the same time, each select The order of the columns of the statement must be the same .

select A.*
from
(
	SELECT 1 flag,t.id,t.name,t.status,t.task_type,u.nickname,t.create_time,t.end_time,t.start_time,t.creator
	from camas_survey_task t,system_user u
	where t.status = 3 and t.deleted = 0 and t.creator = u.id
	union all
	select 2 flag,mr.id,mr.name,mr.status,-1 task_type,u.nickname,mr.create_time,mr.end_time,mr.start_time,mr.creator
	from camas_survey_monitor_rule mr,system_user u
	where mr.status = 3 and mr.deleted = 0 and mr.creator = u.id
)A
order by A.start_time asc