Question

I have a table TestTable:

IntCol
1
4
6
2
3
8
12
11
9
7
15
13
14

(numbers are from 1 to 15 excluding 10).

When I do…

SELECT * FROM 
    (SELECT IntCol
    FROM TestTable
    WHERE IntCol >= 10
    ORDER BY IntCol ASC) x1
UNION ALL
SELECT * FROM 
    (SELECT IntCol
    FROM TestTable
    WHERE IntCol < 10
    ORDER BY IntCol DESC) x2

… result is ok (first from 11 to 15 ASCending, then from 1 to 9 DECSending):

IntCol
11
12
13
14
15
9
8
7
6
4
3
2
1

But when I omit SELECT * FROM and do…

    (SELECT IntCol
    FROM TestTable
    WHERE IntCol >= 10
    ORDER BY IntCol ASC)
UNION ALL
    (SELECT IntCol
    FROM TestTable
    WHERE IntCol < 10
    ORDER BY IntCol DESC)

… rows aren’t ordered at all (only values greater then 10 are first). The result is:

IntCol
12
11
15
13
14
1
4
6
2
3
8
9
7

My question is: why there is this SELECT * FROM needed when UNIONing ordered rows?

Answer 1

Individual Queries, cannot have Order By clause when there is a union in between them.

for reference

http://p2p.wrox.com/sql-language/17907-union-order.html

here is an example of how Order By is used with Union

http://www.techonthenet.com/sql/union.php