How to acheive looping in SQL

Question

Hi Have below requirement,
a.     Take the first 7 digits of a Number string and multiply the 1st digit by 8, the 2nd digit by 7 .....etc..... the 6th digit by 3 and the 7th digit by 2;
b.     Sum up the values of the above seven multiplication;
c.     Subtract 97 from the value at b. above until you have a negative number;
d.     Digits 8 and 9 of the number, the “check digits”, will correspond with the absolute value of the negative number determined at c. above.
Example:
Passing input as number specific one, 'SK391313073'
now first 7 digits are 3913130 and perform Sum like this (3*8)+(9*7)+(1*6)+(3*5)+(1*4)+(3*3)+(0*2) [Sum wil be 121]
I have achieved till above through sql,
Now the sum I should subtract with 97 till it get equal with 8th and 9th digit (here I should loop)
in this case
121-97=24 so this is not equal to 73 (last two digits of input)
so now I need to again perform 24-97 which is -73 and abs(-73)=73 so I need to stop here,
All your help is appreciated,,

Answer 1

Here's a basic example of a FOR loop type structure in SQL - the pseudo column level serves as the loop variable.
You can use the WITH clause as "programming blocks" to calculate something specific and re-use the output of that in another "programming block".
The following example demonstrates the basic approach:
SQL> var n varchar2(20)
SQL> exec :n := 'SK391313073';
PL/SQL procedure successfully completed.
// parse the input string as per requirements
SQL> with number_parse as (
  2          select
  3                  level as i,
  4                  substr(:n,level,1) as ch
  5          from    dual
  6          connect by level <= length(:n)
  7  )
  8  select
  9          *
10  from       number_parse
11  /
         I CH
         1 S
         2 K
         3 3
         4 9
         5 1
         6 3
         7 1
         8 3
         9 0
        10 7
        11 3
11 rows selected.
// tad more complex: using this parsing output, determine the 1st 7 digits
SQL> with number_parse as (
  2          select
  3                  level as i,
  4                  substr(:n,level,1) as ch
  5          from    dual
  6          connect by level <= length(:n)
  7  )
  8  select i,ch from (
  9          select
10                  rownum as rno,
11                  n.*
12          from    number_parse n
13          where   ch in ('0','1','2','3','4','5','6','7','8','9')
14  )
15  where      rno between 1 and 7
16  /
         I CH
         3 3
         4 9
         5 1
         6 3
         7 1
         8 3
         9 0
7 rows selected.
// now add the calculation as required
SQL> with number_parse as (
  2          select
  3                  level as i,
  4                  substr(:n,level,1) as ch
  5          from    dual
  6          connect by level <= length(:n)
  7  ),
  8  first_7 as(
  9          select i,ch from (
10                  select
11                          rownum as rno,
12                          n.*
13                  from    number_parse n
14                  where   ch in ('0','1','2','3','4','5','6','7','8','9')
15          )
16          where   rno between 1 and 7
17          order by i desc
18  )
19  select
20          ch,
21          ch||' * '||to_char(rownum+1)    as calc,
22          to_number(ch)*(rownum+1)        as result
23  from       first_7
24  order by i
25  /
CH  CALC           RESULT
3   3 * 8              24
9   9 * 7              63
1   1 * 6               6
3   3 * 5              15
1   1 * 4               4
3   3 * 3               9
0   0 * 2               0
7 rows selected.
SQL> So SQL is capable of a FOR loop and similar type of (basic) processing that one can do in PL/SQL. However, the SQL language is not Turing Complete, and things can get messy with the above approach, in comparison with doing it in PL/SQL instead.