Order by lower()

Question

I have table T defined below. I sort data with "order by lower(t.VAL)". My question is:
Is there any certain rule how "equal for such order by" records are ordered?
Is it maybe always so, that records with 'a' comes always firstly, and 'A' after those?
Is it maybe always so that records with 'a' are ordered by table primary key?
Or is it so that records are ordered randomly always?
Or are they always ordered in certain way, then define this rule/way.
with T as
(select 3 ID, 'a' VAL from dual union all
select 2 ID, 'A' VAL from dual union all
select 1 ID, 'a' VAL from dual)
select * from T
order by lower(t.VAL);
3     a
1     a
2     A
*/Edited by: CharlesRoos on Apr 16, 2010 4:42 AM
Edited by: CharlesRoos on Apr 16, 2010 4:42 AM

Answer 1

Hi,
CharlesRoos wrote:
I have table T defined below. I sort data with "order by lower(t.VAL)". My question is:
Is there any certain rule how "equal for such order by" records are ordered?
Is it maybe always so, that records with 'a' comes always firstly, and 'A' after those?
Is it maybe always so that records with 'a' are ordered by table primary key?
Or is it so that records are ordered randomly always?
Or are they always ordered in certain way, then define this rule/way.
with T as
(select 3 ID, 'a' VAL from dual union all
select 2 ID, 'A' VAL from dual union all
select 1 ID, 'a' VAL from dual)
select * from T
order by lower(t.VAL);
3     a
1     a
2     A
When you say "ORDER BY x", and x is not unique, there is no guarantee that the rows with the same x will be in any particular order. You may get a certain set of results, then, if you run the exact same query again, without changing the table, get different results.
The order isn't really random, but it is arbitrary. In practice, especially with small tables, you will tend to get the same results, so you might think there is some rule, but the only rule is that no order is guaranteed.
If you want rows in a certain order, add more ORDER BY expressions to break the ties.
For example:
ORDER BY  LOWER (val)          -- 'A' and 'a' together, before 'B' and 'b'
,       val          DESC     -- 'a' before 'A'
,       id