Oracle PL/SQL Exceptions

Exceptions in Oracle are powerful error handling mechanism. Do you feel little difficulty hearing the word Exception handling? This page depicts Exception handling and gives you very clear understanding of error handling in Oracle PL/SQL. I have also explored some myths about exception which often confuses us.

Why & when exception handling are needed?

The errors occurred during the execution of a PL/SQL is called run time error. In general, run time errors are abnormal & crucial which causes your pl/sql program or task uncompleted. So, in general or by standards, it was a good practice to anticapte them and record a log of them. This is where the role of exceptions comes in your pl/sql.

Exception

Exception in Oracle are the error handling section. When ever there is a run time error occurs in your pl/sql code, the execution jumps to your exception block.

Exception section in your pl/sql code should be inside your BEGIN section and placed above END. Below is the syntax of a PL./SQL block using exception.

DECLARE
    ...........
BEGIN
   ...........
EXCEPTION
     WHEN exception_name THEN
         ................
END;
 
 
Where exception_name is oracle defined and below are few examples.
NO_DATA_FOUND - Occurred when a SELCT INTO returns no rows.
VALUE _ERROR  - Occurred when a value assigned is more than 
                defined size or of different datatype.
 

Refer below example, the pl/sql code terminates abnormally wihout a exception block.

declare 
   v_char varchar2(5) ; 
begin 
   v_char := 'Sample Text'; 
   dbms_output.put_line(v_char); 
end; 
 
Error report: 
ORA-06502: PL/SQL: numeric or value error: character string buffer
too small ORA-06512: at line 4 
06502. 00000 - "PL/SQL: numeric or value error%s"

Refer below example, when ever a exception occurs, pl/sql code is completing with a trapped message instead of terminating abnormally.

declare 
   v_char varchar2(5) ; 
begin 
   v_char := 'Sample Text'; 
   dbms_output.put_line(v_char); 
EXCEPTION 
   WHEN VALUE_ERROR THEN 
     dbms_output.put_line('Hi There! 
                       The value supplied is too large!'); 
end;
 
anonymous block completed 
Hi There! The value supplied is too large!

Some myths about Exception

Exception works only for the code after BEGIN. If there are any erros in DECLARE section of your code, it will not be handled by exception. Refer below example.

declare
  v_char varchar2(5) := 'Sample Text';
begin
  dbms_output.put_line(v_char);
Exception
  when no_data_found then
     dbms_output.put_line('Inside no_data_found:' || sqlerrm);
  when value_error then
     dbms_output.put_line('Inside value_error:' || sqlerrm);
  when others then
     dbms_output.put_line('Inside others_found:' || sqlerrm);end;
Error report:

ORA-06502: PL/SQL: numeric or value error: character string buffer too small ORA-06512: at line 2

06502. 00000 - "PL/SQL: numeric or value error%s"

I would suggest writing variable initialiization separately is a best practice. Refer below example which would make sense instead of the above code.

declare 
   v_char varchar2(5);-- := 'Sample Text'; 
begin 
 
   v_char := 'Sample Text'; 
   dbms_output.put_line(v_char);
 
Exception 
   when no_data_found then 
      dbms_output.put_line('Inside no_data_found:' || sqlerrm); 
when value_error then 
dbms_output.put_line('Inside value_error:' || sqlerrm); 
when others then 
dbms_output.put_line('Inside others_found:' || sqlerrm); 
end;
 
anonymous block completed 

Inside value_error:ORA-06502: PL/SQL: numeric or value error: character string buffer too small

Expect more topics on user defined exception and more interesting facts on exceptions with my hub.

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Comments 2 comments

M.A.Anwar 6 years ago

Examples are great. Exception handling in oracle is strong and you have shown it.


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selvirajan 5 months ago from India Author

Thanks for encouraging.

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