MySql：保留 UNION ALL 结果中的顺序

Question

I have the following:

with
result1 as ( select column1 from table1 order by ... )
result2 as ( select column1 from table2 order by ... )
select * from result1 union all select * from result2;

The intent is to list result1 with its order preserved followed by result2 with its order preserved . However, it appears that union all does not preserve the order of its operand tables. How can I get the intended effect? I have tried adding columns to the ordered result1 and result2 and then order the union result on this added column, but this seems awfully klugy for something that seems pretty typical. Is there anything like union all ordered ?

Answer 1

Ok. Here is how you sort it out with "window functions". Provided you are using MySQL 8+

with
result1 as ( 
select column1, ROW_NUMBER() OVER (ORDER BY ...) AS rownum1, 0 AS rownum2, 
from table1 order by ...
),
result2 as ( 
select column1, 0 AS rownum1, ROW_NUMBER() OVER (ORDER BY ...) AS rownum2
from table2 order by ...
),
result as (
select * from result1 
union all
select * from result2 
)
     
select * from result order by rownum2, rownum1