Choose attribute from cursor dynamically

Question

dear forum,
unfortunately, i'm anything but a pl/sql expert, but i have to solve a problem, using pl/sql - and it took me 2 days already, without success :?
problem:
i have a table with the following columns ->
| A1 | B1 | C1 | A2 | B2 | C2 | ...
unfortunately the numbering is no joke the column names really are like: INTERNES_KNZ_1, INTERNES_KNZ_2, etc.
from this one i need to fill another table in the following way ->
A1 | B1 | C1
A2 | B2 | C2
A3 | B3 | C3
so, i made a cursor, like the following:
cursor cur is
          select distinct
               A1, B1, C1, A2, B2, C2
          from TABLE
          where X = 123456
          and Y = 100;
and instead of repeating the following insert-code for all the different attributes
for my_cursor in cur loop
     A1     :=(my_cursor.A1);
     B1     :=(my_cursor.B1);
     C1     :=(my_cursor.C1);
     insert into TABLE_NEW values (A1, B1, C1);
     A2     :=(my_cursor.A2);
     B2     :=(my_cursor.B2);
     C2     :=(my_cursor.C2);
     insert into TABLE_NEW values (A2, B2, C2);
end loop;
i wanted to create a loop ->
i := 2;
A := 'my_cursor.A';
     B := 'my_cursor.B';
     C := 'my_cursor.C';
loop
exit when i<1;
sql_stmt := 'insert into TABLE_NEW values (:1, :2, :3)';
i_string := to_char( i, '9');
Ax := A || to_char(i, '9');
     Bx := B || to_char(i, '9');
     Cx := C || to_char(i, '9');
execute immediate sql_stmt using Ax, Bx, Cx;
i := i-1;          
end loop;
this of course doesn't work because TABLE_NEW expects varchar2 as attribute type and instead of evaluating the variables, 'A1', 'B1', 'C1', etc. is written into the table columns - even though i didn't put quotes (') around.
any ideas how i could solve this?
if it is possible to evaluate a string as a statement?
something like:
     attribute := execute immediate Ax;
which doesn't work, of course.
any help would be much appreciated!!!
and please don't ask me why i really have to do this - there is a good reason for it, but explaining would be rather difficult ;-)
Thanks,
Bianca

Answer 1

Dear forum
Please take a minute (or two ;-)) to read the following and hopefully my question(s) will make more sense to you afterward.
Line: -----
TABLE1
|A_1 | B_1|C_1|A_2|B_2|C_2|...|A_n|
|D|     E|     F|     G|     H|     I|          1|
|D|     E|     F|     G|     H|     I|          2|
|D|     E|     F|     G|     H|     I|          n|
|E|     F|     G|     H|     I|     D|          1|
|E|     F|     G|     H|     I|     D|          2|
|E|     F|     G|     H|     I|     D|          n|
This is the original table, which is filled without my influence – so I have to take it the way it is. It contains a very large set of data, which we need to create rules for our application. The rules are composed of:
the X_1 attributes + A_n
the X_2 attributes + A_n
until the X_n-1 attributes + A_n
The approach my former colleague took, was to create a cursor with all relevant attributes and ALL columns and extract the X_n attributes separately from each row and pair it with the A_n attribute and put it into another table. In the beginning, TABLE1 was small and everything worked fine. But now, when we generate the rules, we have to go through a huge table (which is NOT normalized) and it takes far to long.
So what I’m trying to do is the following:
cursor myCursor1 is
select distinct A_1, B_1, C_1, A_2, B_2, C_2, … C_n-1
from table1
where criterion = criterion_n;
From each row I extract these distinct A to C triples and put them into a new table with a rule number and some other relevant stuff :
TABLE2
|Rule#| Attribute1|     Attribute2| Attribute3|
|011|     D|     E|     F|
|012|     G|     H|     I|
|021|     E|     F|     G|
|022|     H|     I|     D|
Then I declare another cursor within the first one
cursor myCursor2 is
     select t1.A_n
     from table1 t1
     where t1.A_1 = myCursor2.A_1
AND t1.A_2 = myCursor2.A_2
AND t1.A_3 = myCursor2.A_3;
and select all A_n attributes which exist for the current row of the first cursor and put them into another table:
TABLE3
|Rule#| A_n|
|011|     1|
|011|     2|
|011|     n|
|012|     1|
|012|     2|
|012|     n|
|021|     1|
|021|     2|
|021|     n|
|022|     1|
|022|     2|
|022|     n|
All this works fine, but now comes the point where I very much need your help:
Depending on the criterion used for the first cursor (where criterion = criterion_n) the A_n attribute can be at A_3, A_4 or A_5 and I cannot exclude the possibility that some day it will be A_2 or A_6. So what I want is a more generic approach to the whole problem. And I wanted to make some use of the ‘horrible’ fact that the column names in TABLE1 are numbered – something like that:
determine criterion n
then do all the above described with attributes 1 to n-1 and use A_n
And my idea was to use dynamic SQL and pass different values to the cursors, depending on the criterion – but I didn’t manage to do that…
Something like:
begin
i := criterion;
attributeStringA := 'myCursor1.A_';
attributeStringB := 'myCursor1.B_';
attributeStringC := 'myCursor1.C_';
loop
exit when i<1;
sql_stmt := 'insert into table2 values (:1, :2, :3)';
i_string := to_char( i, '9');
A_i := attributeStringA || i_string;
B_i := attributeStringB || i_string;
C_i := attributeStringC || i_string;
my_kennzeichen := cast(internes_knz_x as %type);
execute immediate sql_stmt using A_i, B_i, C_i;
i := i-1;
end loop;
end;
But this doesn’t work, because the respective attributes in TABLE2 expect a varchar2 and thus the strings ‘A_i’, ‘B_i’, ‘C_i’ are written into TABLE2 instead of the values represented by the variables – even though I didn’t put them into quotes.
I’m very sorry for posting all this stuff, even though I have only a basic question about passing variable values to a dynamic SQL statement, but I thought it’s important for you to know why I’m doing what I’m doing ;-) And maybe you see a better/easier way of doing all this.
Thank you very much in advance!
Bianca
Edited by: user11953491 on 13.10.2009 03:09
Edited by: user11953491 on 13.10.2009 03:11
Edited by: user11953491 on 13.10.2009 03:13
Edited by: user11953491 on 13.10.2009 03:13