Doubt in Decode and Using Temporary variable

Question

I was facing the following issue,
For example,
The column_name if A should be stored with the value B or, with itself for which I included a statement as following,
Case [1]
SELECT ....DECODE(column_name,'A','B',column_name) alias_name
     FROM table_name
          WHERE condition;
But,
when i used a temporary variable as following i could not get the expected change,
Case [2]
SELECT ...column_name
     FROM table_name
          WHERE condition;
temp VARCHAR(10);
BEGIN
IF column_name='A' THEN
     temp:='B';
ELSE
     temp:=column_name;
END IF;
END;
I was able to get the right output in Case[1],but failed to get in [2]. Please help and Thanks in advance.

Answer 1

Without seeing your code, whatever I can say might be just an assumption. I can give an example to show that it will work.
SET SERVEROUTPUT ON
DECLARE
  var      VARCHAR2(10);
  col_name VARCHAR2(30);
  TEMP     VARCHAR2(20);
BEGIN
  SELECT column_name
  INTO col_name
  FROM user_tab_columns
  WHERE table_name = 'EMP'
  AND rownum       =1;
  IF (col_name     ='EMPNO') THEN
    temp          := 'X';
  ELSE
    temp := col_name;
  END IF;
  var := 'abc '||temp;
  dbms_output.put_line(var);
END;
OUTPUT :
abc X
PL/SQL procedure successfully completed.