How to check updating of column value in oracle trigger - sql

Question

I'm using UPDATING(col_name) to check if column's value is updated or not inside the trigger. But the big problem is this command won't check value of :old and :new objects. UPDATING(col_name) is true if col_name existed in set part of query even with old value.
I don't want to check :old.col1<>:new.col1 for each column separately.
How can I check changing column value correctly?
I want to do this in a generic way. like :
SELECT col_name bulk collect INTO included_columns FROM trigger_columns where tbl_name ='name';
l_idx := included_columns.first;
while (l_idx is not null)
loop
IF UPDATING(included_columns(l_idx)) THEN
//DO STH
return;
END IF;
l_idx := included_columns.next(l_idx);
end loop;
Thanks

Answer 1

IN a comment you said:
"I want to do this in a generic way and manage it safer. put columns which are important to trigger in a table and don't put many IF in my trigger. "
I suspected that was what you wanted. The only way you can make that work is to use dynamic SQL to assemble and execute a PL/SQL block. That is a complicated solution, for no material benefit.
I'm afraid I laughed at your use of "safer" there. Triggers are already horrible: they make it harder to reason about what is happening in the database and can lead to unforeseen scalability issues. Don't make them worse by injecting dynamic SQL into the mix. Dynamic SQL is difficult because it turns compilation errors into runtime errors.
What is your objection to hardcoding column names and IF statements in a trigger? It's safer because the trigger is compiled. It's easier to verify the trigger logic because the code is right there.
If this is just about not wanting to type, then you can generate the trigger source from the data dictionary views (such as all_tab_cols) or even your own metadata tables if you must (i.e. trigger_columns).

Answer 2

You can define a global function similar to the following:
CREATE OR REPLACE FUNCTION NUMBER_HAS_CHANGED(pinVal_1 IN NUMBER,
pinVal_2 IN NUMBER)
RETURN CHAR
IS
BEGIN
IF (pinVal_1 IS NULL AND pinVal_2 IS NOT NULL) OR
(pinVal_1 IS NOT NULL AND pinVal_2 IS NULL) OR
pinVal_1 <> pinVal_2
THEN
RETURN 'Y';
ELSE
RETURN 'N';
END IF;
END NUMBER_HAS_CHANGED;
Now in your trigger you just write
IF NUMBER_HAS_CHANGED(:OLD.COL1, :NEW.COL1) = 'Y' THEN
-- whatever
END IF;
Note that this function is defined to return CHAR so it can also be called from SQL statements, if needed - for example, in a CASE expression. Remember that in Oracle, there is no BOOLEAN type in the database - only in PL/SQL.
You'll probably want to create additional versions of this function to handle VARCHAR2 and DATE values, for a start, but since it's a matter of replacing the data types and changing the name of the function I'll let you have the fun of writing them. :-)
Best of luck.