How to catch PL/SQL: ORA-00904 error?

Question

Hi ,
I am trying to run the following PL/SQL Block and have trapped error code -904( for invalid column name) in the exception section block.
The column name in the select query does not exist in the emp table and as per my understanding since I have an exceptiion handler for this error it should be handled in Exception Block.
DECLARE
invalid_column exception;
pragma exception_init (invalid_column,-00904);
no number;
BEGIN
select empn into no from emp
where ename='king';
EXCEPTION
when invalid_column then
dbms_output.put_line(Column ane does not exist)
end;
1) Can You please let me know why this is not getting caught in Exception handler
*2) What changes should I make in Exception handler section so that Invalid column name is handled in the program*
Thanks and regards
Harmeet

Answer 1

Check this:
SQL> ed
Wrote file afiedt.buf
  1  DECLARE
  2  invalid_column EXCEPTION;
  3  PRAGMA EXCEPTION_INIT(invalid_column,-00904);
  4  v_col_check NUMBER := 0;
  5  v_col_name VARCHAR2(10) := 'OWNE';
  6  BEGIN
  7  select COUNT(*) INTO v_col_check
  8  from all_tab_cols
  9  where table_name = 'ALL_OBJECTS'
10  AND column_name = v_col_name;
11  IF (v_col_check = 0) THEN
12  RAISE invalid_column;
13  END IF;
14  EXCEPTION
15  WHEN invalid_column THEN
16  DBMS_OUTPUT.PUT_LINE('Column '||v_col_name ||' does not exist in table all_objects');
17* END;
SQL> /
Column OWNE does not exist in table all_objects
PL/SQL procedure successfully completed.
SQL> This way you can check if the column is valid or not in case you are dynamically getting the column names