Oracle Exception Handling - Is this correct? - oracle

Question

I have the following...
IF CONDITION1 THEN
-- SELECT STATEMENT MIGHT RETURN DATA
IF CONDITION2 THEN
-- SELECT COUNT
IF CONDITION3 THEN
INSERT INTO TABLE
(
---
)
VALUES (
---
);
End IF;
END IF;
END IF;
EXCEPTION
WHEN NO_DATA_FOUND THEN
RETURN;
END of Trigger
Is this a correct way of handling exception for select statement inside CONDITION1?

Answer 1

PL/SQL has no way to return to the site of the error, so you need to create a block around the portion you want to ignore specific errors:
IF CONDITION1 THEN
BEGIN
-- SELECT STATEMENT MIGHT RETURN DATA
EXCEPTION
WHEN NO_DATA_FOUND THEN
NULL;
END;
IF CONDITION2 THEN
-- SELECT COUNT
IF CONDITION3 THEN
INSERT INTO TABLE
(
---
)
VALUES (
---
);
End IF;
END IF;
END IF;
END TRIGGER_NAME;
An alternative is to use an explicit cursor, which does not return an error when it is empty:
DECLARE
CURSOR cur_sample is select dummy from dual where 1=0;
v_dummy dual.dummy%type;
BEGIN
IF CONDITION1 THEN
open cur_sample;
fetch cur_sample into v_dummy;
close cur_sample;
IF CONDITION2 THEN
-- SELECT COUNT
IF CONDITION3 THEN
INSERT INTO TABLE
(
---
)
VALUES (
---
);
End IF;
END IF;
END IF;
END;

Answer 2

Depends what you mean by "correct". What you have presented is syntactically valid, yes. But you haven't told us what you actually want to happen so we can't tell you whether the code you posted will actually do what you want.
From a business logic standpoint, are you certain that it really is not an error if your SELECT INTO returns 0 rows? If you are catching and swallowing an exception, that means that you know that it's not really an error. If you're coding a SELECT INTO, however, that implies that you expect exactly one row. It's certainly possible that both of these statements are true but it would be more common that it really is an exception and that it shouldn't simply be swallowed and ignored.
In general, I would prefer to put the exception handler as close as possible to the query that might throw the exception as possible. I would find it cleaner to have something like
IF condition1
THEN
BEGIN
<<select statement>>
EXCEPTION
WHEN no_data_found
THEN
<<do something>>
END;
IF condition2
THEN
...
END IF;
END IF;
That way, if you end up with multiple places in your procedure where a NO_DATA_FOUND exception might be thrown, it will be clear which exceptions are expected and which are unexpected.
When you get to the point of having three layers of nested IF statements, I would tend to suspect that you want to refactor the code into multiple procedures to make the code clearer. For example, rather than having a nested PL/SQL block that executes the SELECT statement, catches the exception, and handles the exception, it would probably be clearer to have a separate function that did all that and then call that function from your trigger.