Oracle PL/SQL dynamic if statement global vars - oracle

Question

I'm having trouble with dynamic sql, Issue is (I think) reading and setting global variable. Here's what I have and any help at all is greatly appreciated. Please let me know if you need table data too although I have included the data in comments.
CREATE OR REPLACE PACKAGE data_load
IS
curr_rec NUMBER;
curr_rule VARCHAR2(200);
curr_sql VARCHAR2(4000);
curr_sql_two VARCHAR2(4000);
curr_data_element VARCHAR2 (200);
curr_rule_text VARCHAR2(200);
curr_error_code VARCHAR2(10);
curr_error_flag VARCHAR2(10);
curr_flag_val NUMBER;
v_check NUMBER;
v_ID NUMBER;
cur_hdl INT ;
rows_processed NUMBER;
PROCEDURE check_rules;
END data_load;
The package body:
create or replace PACKAGE BODY data_load IS
PROCEDURE check_rules IS
CURSOR c1
IS
SELECT * FROM STAGING_TABLE where rownum < 3;
CURSOR c2
IS
SELECT * FROM ERROR_CODES WHERE rule_text IS NOT NULL AND status =1;
BEGIN
FOR rec1 IN c1
LOOP
FOR rec2 IN c2
LOOP
curr_data_element := 'rec1.'||rec2.data_element; --- this results in value "rec1.SHIP_FROM_ACCOUNT_ORG_CODE" without quotes
curr_rule_text := rec2.rule_text; --- this value is "is not null" without quotes
curr_error_flag := rec2.error_flag; --this value is "FLAG_03" without quotes
curr_flag_val := to_number(rec2.error_code); --- this value is 31
curr_sql :='begin if :curr_data_element '||curr_rule_text||' then update table_with_column_FLAG_03 set '||curr_error_flag ||' = 0; else update table_with_column_FLAG_03 set '||curr_error_flag ||' = '||curr_flag_val||'; end if; end;';
dbms_output.put_line(curr_sql); -- results in "begin if :curr_data_element is null then update table_with_column_FLAG_03 set FLAG_03 = 0; else update table_with_column_FLAG_03 set FLAG_03 = 31; end if; end;"
EXECUTE IMMEDIATE curr_sql USING curr_data_element ; -- this always updates the column with 31 even when curr_data_element/ rec1.SHIP_FROM_ACCOUNT_ORG_CODE is null and that's the problem
COMMIT;
END LOOP;
curr_rec := curr_rec+1;
END LOOP;
dbms_output.put_line(curr_rec);
END check_rules;
END data_load;

Answer 1

You've already highlighted the problem really:
curr_data_element := 'rec1.'||rec2.data_element; --- this results in value "rec1.SHIP_FROM_ACCOUNT_ORG_CODE" without quotes
You can't refer to cursor columns dynamically. You are creating a string with value 'rec1.SHIP_FROM_ACCOUNT_ORG_CODE'; there is no mechanism to evaluate what that represents. You can't, for instance, try to dynamically select that from dual because the rec1 is not in scope for a SQL call, even dynamically.
When you bind that string value it is never going to be null. You are using that string, not the value in the outer cursor that it represents, and essentially you cannot do that.
The simplest way to deal with this, if you have a reasonably small number of columns in your staging table that might appear as the rec2.data_element value, is to use a case expression to assign the appropriate actual rec1 column value to the curr_data_element variable, based on the rec2.data_element value:
...
BEGIN
FOR rec1 IN c1
LOOP
FOR rec2 IN c2
LOOP
curr_data_element :=
case rec2.data_element
when 'SHIP_FROM_ACCOUNT_ORG_CODE' then rec1.SHIP_FROM_ACCOUNT_ORG_CODE
when 'ANOTHER_COLUMN' then rec1.ANOTHER_COLUMN
-- when ... -- repeat for all possible columns
end;
curr_rule_text := rec2.rule_text;
...
If you have a lot of columns you could potentially do that via a collection but it may not be worth the extra effort.
The curr_sql string stays the same, all that's changing is that you're binding the actual value from the relevant rec1 column, rather than never-null string you were forming.