URGENT : replacing some letters in an expression

Question

Hi all
I think that I should post this topic here because I think it concerns SQL and PL/SQL functions. Here is the problem :
I am developping a forms application . There is a listbox named FORMULA containing list of formulas. When I choose a formula from that list then there is a program which exctracts all of its operands. For example if the formula is : (a+b)*abs(c-d) then the operands are : a,b,c and d.
Then I populate another listbox named OPERANDS with these operands. So the value of the OPERANDS listbox is either a or b or c or d in our example.
I held the expression of the formula in a global variable so it can be accessible anywhere in my application.
When I choose one of the operands from the OPERANDS listbox , for example b,then I enter its value , for example 5, in a text field named VALUE ,and then I click on a button to replace the letter "b" in the formula with the value I entered , which is 5. So I want to get an expression like this : (a+5)*abs(c-d) .
But the problem is that when I run the application then all letters "b" in the formula are replaced by 5 . So even the expression "abs", which is a pl/sql function, is replaced by "a5s". And I do not want that to happen.
Here is how I proceeded :
formula := replace(formula,operands,value); where "formula" is the global variable containing the formula expression, "operands" is the variable containing the value of the OPERANDS listbox which is "b" here, and "value" is the variable containing the value 5.
So how can I avoid this misreplacement ?
Thank you very much indeed.

Answer 1

select
   e,
   regexp_replace(
      regexp_replace(e,
      '([^[:alnum:]_]|^)b([^[:alnum:]_(]|$)','\15\2'
      ),'([^[:alnum:]_])b([^[:alnum:]_(]|$)','\15\2'
   ) "EXP"
from
   (select '(a+b)*abs(c-d)' e from dual
   union select 'b+b' from dual
   union select 'b+b+b+b' from dual
   union select '1-b(b)' from dual)
E              EXP
(a+b)*abs(c-d) (a+5)*abs(c-d)
1-b(b)         1-b(5)
b+b            5+5
b+b+b+b        5+5+5+5If you do not have 10g, you can look at the OWA* packages or write you own function
Regards
Laurent