Sorting: ORDER BY DECODE Problem on Pagination Query

Question

Hi,
I've been searching around the easiest way to perform a dynamic "ORDER BY" clause and the "DECODE()" clause solution seem to be exactly what I am looking for. Unfortunately, It seems the DECODE function is not returning a correct column name value (I think it is returning NULL) since I'm receive the result set as if there was no ORDER BY clause.
I need some help to get through this!
Here the version with DECODE (not working)
It is a Procedure with frstRow, nbRows and var_order as parameters
The output returns the rows as if no ORDER BY was used
SELECT c1, c2
FROM
SELECT ROWNUM rn, arv.*
FROM A_AWA_AR arv
WHERE ROWNUM < (frstRow + nbRows - 1) -- show only some rows determined by procedure
ORDER BY DECODE(var_order, 1, c1, 2, c2, c1) -- sort by var_order
WHERE rn BETWEEN frstRow AND (frstRow + nbRows)
AND ROWNUM <= nbRows
Here the version without DECODE (working)
The output returns the rows as expected - ordered by c2 column
SELECT c1, c2
FROM
SELECT ROWNUM rn, arv.*
FROM A_AWA_AR arv
WHERE ROWNUM < (frstRow + nbRows - 1) -- show only some rows determined by procedure
ORDER BY c2 -- sort by var_order
WHERE rn BETWEEN frstRow AND (frstRow + nbRows)
AND ROWNUM <= nbRows
-----

Answer 1

Here are some results I've been getting... I will try the best I can to explain my problem.
And by the way the table A_AWA_AR is a VIEW maybe this can help.
My problem -- I think -- is that I don't understand how DECODE works. I should be a conditional IF-ELSE-THEN-like function but its behavior is not returning what I'm expecting.
I need a solution where I will be able to sort the first lets say 10 rows using ROWNUM to tag row position (in sub-query) then the main query should only show the rows from 3rd postion to 7th position in the main query (as an example) with RN BETWEEN 3 AND 7. My solution does not work when I use decode but works when i pass the column name directly.
Here is a simple query returning the values in the order they are found in the view:
SELECT ROWNUM rn, ROW_ID, SR_NUM
FROM A_AWA_AR
WHERE ROWNUM < 10 Results:
RN                                     ROW_ID          SR_NUM                                                         
1                                      1-100876        1-60476802                                                     
2                                      1-10087G        1-60476812                                                     
3                                      1-10087Q        1-60476822                                                     
4                                      1-10088A        1-60476842                                                     
5                                      1-10088K        1-60476852                                                     
6                                      1-10088U        1-60476862                                                     
7                                      1-100894        1-60476872                                                     
8                                      1-10089E        1-60476882                                                     
9                                      1-10089O        1-60476892                                                      Now this is the query & result I would like to obtain (this is done pretty fast since it returns as soon as it reaches 9 sorted rows):
SELECT ROWNUM rn, ROW_ID, SR_NUM
FROM A_AWA_AR
WHERE ROWNUM < 10
ORDER BY SR_NUMResults:
RN                                     ROW_ID          SR_NUM                                                         
1                                      1-1RV9J7        1-107274499                                                    
2                                      1-1RVXIF        1-107305575                                                    
3                                      1-1SHY65        1-108332861                                                    
4                                      1-22FOSR        1-125023563                                                    
5                                      1-236F3X        1-126270717                                                    
6                                      1-28P5EB        1-135542675                                                    
7                                      1-29P2VY        1-137219038                                                    
8                                      1-29ZNFH        1-137712221                                                    
9                                      1-2BLWQR        1-140430339                                                     But with decode even a simple pseudo decode:
SELECT ROWNUM rn, ROW_ID, SR_NUM
FROM A_AWA_AR
WHERE ROWNUM < 10
ORDER BY DECODE(1,1,SR_NUM)Results:
RN                                     ROW_ID          SR_NUM                                                         
1                                      1-100876        1-60476802                                                     
2                                      1-10087G        1-60476812                                                     
3                                      1-10087Q        1-60476822                                                     
4                                      1-10088A        1-60476842                                                     
5                                      1-10088K        1-60476852                                                     
6                                      1-10088U        1-60476862                                                     
7                                      1-100894        1-60476872                                                     
8                                      1-10089E        1-60476882                                                     
9                                      1-10089O        1-60476892                                                      Here is the structure I'm trying to get and works when passing a column name:
SELECT *
FROM
    SELECT ROWNUM rn, ROW_ID, SR_NUM
    FROM A_AWA_AR
    WHERE ROWNUM < 10
    ORDER BY SR_NUM
WHERE rn BETWEEN 3 AND 7Results:
RN                                     ROW_ID          SR_NUM                                                         
3                                      1-1SHY65        1-108332861                                                    
4                                      1-22FOSR        1-125023563                                                    
5                                      1-236F3X        1-126270717                                                    
6                                      1-28P5EB        1-135542675                                                    
7                                      1-29P2VY        1-137219038                                                     Now with decode (not working):
SELECT *
FROM
    SELECT ROWNUM rn, ROW_ID, SR_NUM
    FROM A_AWA_AR
    WHERE ROWNUM < 10
    ORDER BY DECODE(1,1,SR_NUM)
WHERE rn BETWEEN 3 AND 7Results:
RN                                     ROW_ID          SR_NUM                                                         
3                                      1-10087Q        1-60476822                                                     
4                                      1-10088A        1-60476842                                                     
5                                      1-10088K        1-60476852                                                     
6                                      1-10088U        1-60476862                                                     
7                                      1-100894        1-60476872                                                      Thanks for the support!