query inside the exception and begin block in exception - sql

Question

Hello I want to ask what is the best practise to do.
First example try to retrieve my data through exceptions I use this code in my main application and is working fine but I dont know if its good practise to code inside the exceptions blocks
BEGIN
DECLARE
v_status varchar2(100);
v_flag varchcar2(100);
BEGIN
SELECT STATUS INTO v_status FROM TABLE1 WHERE condition1;
EXCEPTION
when no_data_found then
select FLAG INTO v_flag FROM TABLE2 WHERE condition1; -- THERE WILL BE 100% RECORD
IF v_flag='N' THEN
V_STATUS:='N'
ELSIF v_flag:='O'
V_STATUS:='O'
ELSE
BEGIN
SELECT STATUS INTO V_STATUS FROM TABLE3 WHERE condition1,condition2;
EXCEPTION
V_STATUS:='F';
END;
END IF;
END;
IF V_STATUS='O' THEN
--DO SOMETHING HERE
ELSIF V_STATUS='N' THEN
--DO SOMETHING HERE
ELSE
--DO SOMETHING HERE
END IF;
END;
SECOND EXAMPLE TRY TO RETRIEVE DATA WITH CASES AND SELECT WITH COUNT.
BEGIN
DECLARE
V_CNTR NUMBER;
V_STATUS VARCHAR2(100);
BEGIN
SELECT COUNT(1) INTO V_CNTR FROM TABLE1 WHERE condition1;
CASE
WHEN COUNT=1 THEN
SELECT STATUS INTO V_STATUS FROM TABLE1 WHERE condition1;
ELSE
select FLAG INTO v_flag FROM TABLE2 WHERE condition1; -- THERE WILL BE 100% RECORD
IF v_flag='N' THEN
V_STATUS:='N'
ELSIF v_flag:='O'
V_STATUS:='O'
ELSE
SELECT COUNT(1) INTO V_CNTR FROM TABLE3 WHERE condition1,condition2;
CASE
WHEN count=1 THEN
SELECT STATUS INTO V_STATUS FROM TABLE3 WHERE condition1,condition2;
ELSE
V_STATUS:='F';
END CASE;
END IF;
END CASE;
END;
IF V_STATUS='O' THEN
--DO SOMETHING HERE
ELSIF V_STATUS='N' THEN
--DO SOMETHING HERE
ELSE
--DO SOMETHING HERE
END IF;
END;

Answer 1

From personal experience...
Those nested blocks work fine and it can be useful to use code in exception blocks, but it becomes very unreadable quickly as you show in your example. If your initial code looks like this, then imagine what it will look like a couple of development cycles later.
It is cleaner to move those BEGIN SELECT INTO EXCEPTION WHEN NO_DATA_FOUND THEN... END: blocks into functions. Makes the code a lot more structured, more readable and easier to debug and maintain:
DECLARE
v_status varchar2(100);
v_flag varchcar2(100);
FUNCTION status (argument_i VARCHAR2) RETURN VARCHAR2
IS
l_status VARCHAR2(100);
BEGIN
SELECT STATUS INTO v_status FROM TABLE1 WHERE condition = argument_i;
EXCEPTION WHEN NO_DATA_FOUND THEN
RETURN NULL; -- or -1 or NOTFOUND - whatever you prefer
END;
BEGIN
v_status := status(argument_i => condition);
IF v_status IS NULL THEN
...
ELSE
...
END IF;
END;
Here it's an inline function - within packages you can use standalone functions, private if never called outside the package.
Note, in your 2 examples you declare the variables in the inner block but call them in the outer block - that is something to avoid.

Answer 2

The best practice is always to keep your code clean and readable.
To keep your code clean and readable, make it well structured.
To make it well structured, you have to split code in units where each unit does one thing - has one responsibility.
Read more on SOLID principles, DRY principle to get the idea.
Short answer to your question: coding in exception blocks is not the best practice I'd follow.
Take a look at this presentation on clean PL/SQL coding to get some greater overview.