Combining several query results into one table, how is the results order determined?

Question

I am retuning table results for different queries but each table will be in the same format and will all be in one final table. If I want the results for query 1 to be listed first and query2 second etc, what is the easiest way to do it?

Does UNION append the table or are is the combination random?

Answer 1

UNION appends the second query to the first query, so you have all the first rows first.

Answer 2

The SQL standard does not guarantee an order unless explicitly called for in an order by clause. In practice, this usually comes back chronologically, but I would not rely on it if the order is important.

Across a union you can control the order like this...

select
   this,
   that
from
   (
   select
      this,
      that
   from
       table1
   union
   select
     this,
     that
   from
     table2
   )
order by
   that,
   this;

Answer 3

You can use:

SELECT Col1, Col2,...
FROM (
    SELECT Col1, Col2,..., 1 AS intUnionOrder
    FROM ...
) AS T1
UNION ALL (
    SELECT Col1, Col2,..., 2 AS intUnionOrder
    FROM ...
) AS T2
ORDER BY intUnionOrder, ...