How can I handle this compilation error through exception? - sql

Question

How can I handle this compilation error through exception?
declare
table_or_view_does_not_exist exception;
pragma exception_init(table_or_view_does_not_exist,-00942);
b exception;
pragma exception_init(b,-00942);
d_table varchar2(200);
c_table varchar2(200);
c_count Number;
begin
begin
d_table:='drop table audit_table PURGE';
execute immediate d_table;
exception
when table_or_view_does_not_exist then
null;
end;
<<lable>>
c_table := 'create table audit_table
(table_name varchar2(50),
column_name varchar2(50),
count_type varchar2(50),
v_count number)';
execute immediate c_table;
select count(*) into c_count from customer_profile where cust_id is null;
insert into audit_table columns (table_name,column_name,count_type,v_count) values('customer_profile','cust_id','null','c_count');
exception
when b then
GOTO lable;
end;
Error report:
ORA-06550: line 25, column 13:
PL/SQL: ORA-00942: table or view does not exist
ORA-06550: line 25, column 1:
PL/SQL: SQL Statement ignored
ORA-06550: line 28, column 2:
PLS-00375: illegal GOTO statement; this GOTO cannot branch to label 'LABLE'
ORA-06550: line 28, column 2:
PL/SQL: Statement ignored
06550. 00000 - "line %s, column %s:\n%s"
*Cause: Usually a PL/SQL compilation error.
*Action:

Answer 1

What you do, is just bad practice. In Oracle, we don't create tables in PL/SQL but at SQL level and then use them in our procedures.
In your case, you'd
-- create table first
create table audit_table ...;
-- use it in PL/SQL procedure
declare
...
begin
...
insert into audit_table ...
end;
/
You can't "handle" compilation error through exception. What you could do is to put insert statement into dynamic SQL. Also, it wouldn't harm if you used valid syntax (there's no columns "keyword" there).
execute immediate q'[insert into audit_table
(table_name, column_name, count_type, v_count)
values('customer_profile', 'cust_id', 'null', :a)]'
using c_count;
but - once again - that's just bad practice. Don't do it that way, there's no benefit and many disadvantages.
As of goto - well, jumping around your code is almost always wrong. Error you got says that you can't jump out of the exception handler so your idea was wrong anyway.

Answer 2

You actually can trap compilation errors, by wrapping the whole block in an execute immediate so compilation is postponed until runtime. But that's not the right way to go.
Your real issue is that you are referring to the object you are dynamically dropping/creating as a hard-coded dependency of your PL/SQL block:
insert into audit_table ... -- this is a hard dependency
You can't compile PL/SQL if hard dependencies don't exist until run time. If you really must dynamically drop/recreate the table (and I agree with the above reviewer that this is architecturally questionable), you must also make this insert dynamic as well in order to break the dependency chain:
execute immediate 'insert into audit_table values (:col1, :col2, :col3, :col4)' using 'customer_profile','cust_id','null','c_count'; -- this creates no dependency
That will prevent Oracle from creating an object dependency on this table so your code can compile even though the table does not exist at compile time.
But once again, please be sure this is the right technique. There are only a few rare cases where this actually makes good architectural sense. Oh, and please remove the GOTO and label junk. We really don't use that in modern languages; they create unmanageable spaghetti code.

Answer 3

Could you consider another way to control the flow - comments in the code:
DECLARE
cmd VarChar2(200);
c_count Number(6);
--
Status VarChar2(255);
BEGIN
cmd :='drop table audit_table';
Begin -- 1st nested PL/SQL block
Execute Immediate cmd;
Status := 'OK';
Exception -- this could be raised if the table doesn't exist which is probably OK
When OTHERS Then
Status := 'OK'; -- SQLERRM = ORA-00942: table or view does not exist - nothing happens - it would be droped anyway
-- Status := 'ERR - ' || SQLERRM; -- this is alternative if you want to do something else with this ERR
End;
If Status != 'OK' Then -- here you can check the status and decide what to do
GoTo EndIt;
End If;
--
<<lable>> -- in this code there is no need for this label
cmd := 'create table audit_table (table_name varchar2(50), column_name varchar2(50), count_type varchar2(50), v_count number)';
Begin -- 2nd nested PL/SQL block
Execute Immediate cmd;
Status := 'OK';
Exception
When OTHERS Then
Status := 'ERR - ' || SQLERRM;
End;
If Status != 'OK' Then -- here you can check the status and decide what to do
dbms_output.putline(Status); -- send error message and exit - there is no audit_table
GoTo EndIt;
Else
Null; -- here you can do something else (if maybe the table already exists)
End If;
--
-- think about what could go wrong below (2 lines) and either leave it as it is or put it in the 3rd nested PL/SQL block
Select count(*) Into c_count From customer_profile Where cust_id Is Null;
insert into audit_table (table_name, column_name, count_type, v_count) values('customer_profile', 'cust_id', 'Null', c_count);
<<EndIt>> -- used to end the block if needed
Null;
EXCEPTION
When OTHERS Then
dbms_output.putline(SQLERRM); -- You can not get out of here since it is main PL/SQL blok that went into an exception
END;
Addition
Below is an option of basic steps to do the job (3rd block) without compilation errors. I have no possibility to check it out so please do it yourself (there could be some syntax problem or something else). The goal is to be sure that you can insert the record...
I declared sq variable to construct insert command and the end of the code above could be (please check the command yourself - I can't test it right now) something like here:
DECLARE
...
sq VarChar2(1) := ''''; -- this is single-quote character
...
BEGIN
...
...
--
-- think about what could go wrong below (2 lines) and either leave it as it is or put it in the 3rd nested PL/SQL block
Select count(*) Into c_count From customer_profile Where cust_id Is Null;
cmd := 'insert into audit_table (table_name, column_name, count_type, v_count) values(' || sq || 'customer_profile' || sq || ', ' || sq || 'cust_id' || sq || ', ' || sq || 'Null' || sq || ', ' || c_count || ')';
Begin -- 3rd nested PL/SQL block
Select Count(*) Into c_count From all_tables Where table_name = 'audit_table' and owner = 'your_table_owner'; -- check if table exist - if it doesn't set Status
If c_count = 1 Then -- if table exists then you can insert the record
Execute Immediate cmd;
Status := 'OK'; -- all done
Else
Status := 'ERR';
End If;
Exception
When OTHERS Then
Status := 'ERR - ' || SQLERRM; -- catch error and pass it to the main block
End;
If Status != 'OK' Then -- here you can check the status and decide what to do
dbms_output.putline(Status); -- send error message and exit - there is no audit_table -->> OR DO SOMETHING ELSE
GoTo EndIt;
Else
Null; -- here you can do something else if you wish
End If;
--
<<EndIt>> -- used to end the block if needed
Null;
EXCEPTION
When OTHERS Then
dbms_output.putline(SQLERRM); -- You can not get out of here since it is main PL/SQL blok that went into an exception
END;