Dynamic IF...ELSE

Question

Hi,
I'm having some hard time looking for a way to code some sort of dynamic 'IF..ELSE' statement. The fields and conditions will be coming from the select statement that I will in-store in a PL/SQL table and work through it.
Ex.
Rules (Table)
Field_1 = 'EMP.Employee_Id'
Field_2 = 'DEPT.Employee_Id'
Mathematical_Operation = '='
IF <Field_1> <Mathematical_Operation> <Field_2> THEN
Thus...
IF EMP.Employee_Id = DEPT.Employee_Id THEN
I'm working on 9.2.0.4 database release.
Thanks in advance.

Answer 1

It is possible to dynamically generate PL/SQL. Your problem is, you need to generate the entire program. So, if you are manipulating PL/SQL tables in your dynamic SQL you need to declare those tables and populate them in the dynamic code. Although, I suppose you could pass PL/SQL tables as parameters to EXECUTE IMMEDIATE, I've never tried. Either way, I foresee a gnarly piece of code coming up. I'm glad I don't have to maintain it.
In the following example I shall ignore all considerations of PL/SQL tables, etc. In other words, it won't work but it will give you the idea.
plsql_stmt := 'DECLARE l1 number; l2 number; l3 number; l4 number; BEGIN '
plsql_stmt := plsql_stmt||' l1 := :1; l2 := :2; l3 := :3;';
FOR lrec IN ( SELECT rownum AS r, field_1, field_2, math_op, do_something FROM rules )
LOOP
   IF lrec.r != 1
   THEN
      plsql_stmt := plsql_stmt||'ELSIF ';
   ELSE
      plsql_stmt := plsql_stmt||'IF ';
   END IF;
   plsql_stmt := plsql_stmt||lrec.field_1||' '||lrec.math_op||' '||lrec.field_2;
   plsql_stmt := plsql_stmt||' THEN '||lrec.do_something||' ;';
END LOOP;
plsql_stmt := plsql_stmt||' END IF; :4 := l4; END;';
EXECUTE IMMEDIATE plsql_stmt USING ln_abc, ln_def, ln_ghi, ln_result;
...Good luck, APC