Selecting/Ordering/ROWNUMBER in Oracle 9i

Question

Hello,
I am trying to sort a large table by 'splitting' it in 2 ranges based on the numeric
value of a varchar2 column:
colA=varchar2(7) (represents a numeric range, like a transaction number)
If hypothetically the table has 1000 rows I am trying to split it into 1-500 and 501-1000
then I do:
statement1:
SELECT colA FROM (select rownum AS z,colA from TABLE1 ORDER BY lpad(colA,7) ASC ) WHERE z>=1 and z<501;
statement2:
SELECT colA FROM (select rownum AS z,colA from TABLE1 ORDER BY lpad(colA,7) ASC ) WHERE z>=501 and z<1001;
This is not working: I am finding values of colA in the second statement output that
should be in the first select range based on numeric value
e.g.
Doing MAX(colA) for statement1(lower range) gives 1030240
Doing MIN(colA) for statement 2 (upper range) gives: 1000008
In an ascending sort, the maximum value of colA in statement1 should be LESS than
the minimum value of statement2 using the same sorting criteria.
Why is this not working? It seems the ROWNUMs get jumbled up here...
Does the "inner" select (select rownum AS z,colA from TABLE1 ORDER BY lpad(colA,7) ASC) attribute the ROWNUMs to the ordered set and then lose
the ordering for the outer select?
Any help greatly appreciated...

Answer 1

If you split your table according to lpad(colA,7) - behaves like to_number(ColA)
and then "check" the result by retrieving each range's min(ColA) and max(ColA) - varchar2 type
the "strange" behaviour will not disappear
=========================
ColA  | lpad(ColA,7)
=========================
1     |       1
12    |      12
123   |     123
1234  |    1234
12345 |   12345
23456 |   23456
3456  |    3456
456   |     456
78    |      78
9     |       9
=========================
ColA  | ordered | rownum
=========================
1     |       1 |  1     <= lower range ColA minimum
9     |       9 |  2     <= lower range ColA maximum
12    |      12 |  3        lower range
78    |      78 |  4        lower range
123   |     123 |  5        lower range
456   |     456 |  6        upper range
1234  |    1234 |  7     <= upper range ColA minimum
3456  |    3456 |  8        upper range
12345 |   12345 |  9        upper range
23456 |   23456 | 10     <= upper range ColA maximumRegards
Etbin