I am writing a deployment script that includes a MERGE into a view that may or may not exist in one of many target schemas (schemii? schemata?).
I am attempting this SQL:
DECLARE
BEGIN
/* MERGE statement that will work if the view is available */
EXCEPTION
WHEN OTHERS THAN
DBMS_OUTPUT.put_line('warning: merge target is not available');
END;
When I run this block I get the standard "PL/SQL: ORA-00942: table or view does not exists" error.
How can I trap this error and generate a warning line instead?
Combining the valid answers with the suggested improvements, it all came together as:
SET SERVEROUTPUT ON;
PROMPT ...trying UPSERT;
DECLARE
eTableNotExists exception;
pragma exception_init(eTableNotExists, -00942);
BEGIN
EXECUTE IMMEDIATE '<MERGE statement that will work if the view is available--no trailing ";"!>';
DBMS_OUTPUT.put_line('insert worked');
EXCEPTION
WHEN eTableNotExists THEN
DBMS_OUTPUT.put_line('FYI: doesn''t exist on this schema');
END;
/
COMMIT;
SET SERVEROUTPUT OFF;
(SERVEROUTPUT sets were necessary to see results of DBMS_OUTPUT.put_line())
You need to use dynamic SQL:
BEGIN
EXECUTE IMMEDIATE 'MERGE ...';
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.put_line('warning: merge target is not available');
END;
You can use dynamic SQL to postpone such an error to run time and catch it
EXECUTE IMMEDIATE '<MERGE>'
instead of "static" MERGE
Related
So I made a bug in which I didn't put execute immediate inside nested begin-end block so my code didn't work. So basically I had
begin
execute immediate 'select * from sales';
exception when others then null;
dbms_output.put_line(123);
end;
Dbms_output did not print "123" and I figured out I need to put execute immediate inside begin-end. I want to be sure, so my question is why is code not executing after exception part even though exception is not raised?
why is code not executing after exception part even though exception is not raised?
The reason is very simple - dbms_output.put_line in the question is not in "after exception part".
Properly indented code is equivalent to:
begin
execute immediate 'select * from dual';
exception when others then
null;
dbms_output.put_line(123);
end;
/
Exception block is everything between EXCEPTIONS and END; and will be executed if an exception occurs.
A couple of things in play here - parsing and execution.
If the table does not exist, then the statement cannot be parsed, and hence we'll get an exception immediately.
SQL> begin
2 execute immediate 'select * from xxxx';
3 end;
4 /
begin
*
ERROR at line 1:
ORA-00942: table or view does not exist
ORA-06512: at line 2
However, if the table DOES exist then the parse will be fine. Because you never specified an INTO that is all we do. We never needed to execute and commence the fetch phase and thus no error occurred. An easy to way to see that we never executed the statement is with something like
SQL> begin
2 execute immediate 'select 1/count(*) from dual where 1=2';
3 end;
4 /
PL/SQL procedure successfully completed.
If we had executed, then we'd expect a divide by zero error to come out. The moment we see an INTO, then we'll need to fetch (which will require an execution).
I would like to create the following index
CREATE INDEX timevariable_idx_varvalue_projectid
ON timevariable (varvalue,projectid);
only if does not exist, but I'm having a hard time doing it
would anyone know how to do so?!
Unfortunately Oracle does not support the IF NOT EXISTS clause to CREATE statements (I don't know about APEX though, which you also tagged your question with).
So you need execute immediate in a code block. This Ask TOM article gives an elegant solution that works by trapping exceptions.
Adapted to your use case, this would be:
set serveroutput on
declare
already_exists exception;
columns_indexed exception;
pragma exception_init(already_exists, -955);
pragma exception_init(columns_indexed, -1408);
begin
execute immediate 'create index timevariable_idx_varvalue_projectid ON timevariable (varvalue,projectid)';
dbms_output.put_line('created');
exception
when already_exists or columns_indexed then
dbms_output.put_line('skipped');
end;
Oracle has no "IF NOT EXISTS" syntax in its DDL commands. If you execute the CREATE command, you either need to accept the error in your script as ok to ignore, or handle the error in some way. If you want to avoid the execute commend unless necessary, you'd need to check the data dictionary for the index first, then execute if required:
declare
l_count number;
begin
select count(*) into l_count from dba_indexes where index_name='TIMEVARIABLE_IDX_VARVALUE_PROJECTID';
if l_count = 0 then
execute immediate 'CREATE INDEX timevariable_idx_varvalue_projectid ON timevariable (varvalue,projectid)';
end if;
end;
I have implemented a certain feature in my application where the user can compose queries dynamically from the user interface by pushing around buttons and inserting some values here and there.
The user will not see the generated SQL statement at all.
I was wondering if there is a way to perhaps check the syntax and grammar (e.g. he opened a parantheses '(' and forgot to close it ) of the dynamically generated SQL to ensure that no run-time compilation errors would happen before actually executing the statement using EXECUTE IMMEDIATE.
You could use the dbms_sql.parse procedure to parse the SQL statement assuming the statement is DML not DDL. It would be rather unusual to parse a dynamic SQL statement using the dbms_sql package and then use EXECUTE IMMEDIATE to execute it rather than using dbms_sql.execute but nothing prevents you from mixing dbms_sql and execute immediate.
The code to just parse the SQL statement would be something like
DECLARE
l_cursor integer;
l_sql_stmt varchar2(1000) := <<some SQL statement>>;
BEGIN
l_cursor := dbms_sql.open_cursor;
dbms_sql.parse( l_cursor, l_sql_stmt, dbms_sql.native );
dbms_sql.close_cursor( l_cursor );
END;
You can also use explain plan, this is basically doing the first step of the execution.
SQL> explain plan for select * from dual;
Explained.
SQL is valid, you can also use the explain tables to get the tables, views etc, maybe even estimated run time ...
SQL> explain plan for select * from duall;
explain plan for select * from duall
*
ERROR at line 1:
ORA-00942: table or view does not exist
SQL is invalid, this is why ...
you can also use it in a dynamic statement
SQL> begin execute immediate 'explain plan for ' || ' select * from dual'; end;
2 /
PL/SQL procedure successfully completed.
As always use error-handling, e.g. write a little error log creater package or procedure what u call when it's needed.
DECLARE
my_stmt VARCHAR2(4000):='this will contain my statements';
BEGIN
'begin' || my_stmt || 'end';
EXCEPTION
WHEN OTHERS THEN
prc_my_error_log_creator();
END;
in the log_creator use for example the DBMS_UTILITY.FORMAT_ERROR_BACKTRACE() func to get the stack's contain.
Regards
We have a stored procedure that inserts data into a table from some temporary tables in oracle database. There is an update statement after the insert that updates a flag in the same table based on certain checks. At the end of the stored procedure commit happens.
The problem is that the update works on 95% cases but in some cases it fails to update. When we try to run it again without changing anything, it works. Even trying to execute the same stored procedure on the same data at some other time, works perfectly. I haven't found any issues in the logic in the stored procedure. I feel there is some database level issue which we are not able to find (maybe related to concurrency). Any ideas on this would be very helpful.
Without seeing the source code we will just be guessing. The most obvious suggestion that I can think of is that it hits an exception somewhere along the way in some cases and never gets as far as the commit. Another possibility is that there is a lock on the table during execution when it fails.
Probably the best thing to investigate further would be to add an exception handler that writes the exceptions to some table or file and see what error is raised e.g.
-- create a logging table
create table tmp_error_log (timestamp timestamp(0), Error_test varchar2(1000));
-- add a variable to your procedure declaration
v_sql varchar2(1000);
-- add an exception handler just before the final end; statement on your procedure
exception
when others then
begin
v_sql := 'insert into tmp_error_log values(''' ||
to_char(sysdate, 'DD-MON-YYYY HH24:MI:SS') || ''', ''' || SQLERRM || ''')';
dbms_output.put_line(v_sql);
execute immediate v_sql;
commit;
end;
-- see what you get in the table
select * from tmp_error_log;
Right now I'm importing and transforming data into an Oracle database as follows:
A program regularly polls specific folders, once a file is found it executes a batch file which does some light transformation in Python & bash and then calls SQL*Loader to load the CSV file into a staging table.
Then, the batch script calls an SQL script (via SQLPlus) to do the final transformation and insert the transformed data into master tables for their respective staging table.
The problem with this method is there's no error-handling on the SQLPlus side, eg. if an 'insert into' statement fails because of a violated constraint (or any other reason), it will still continue to execute the rest of the statements contained in the SQL script.
Ideally, if any exception occurs, I'd prefer all changes to be rolled back and details of the exception inserted into an etl log table.
Stored procedures seem to be a good fit as exception handling is built-in. However, I'm struggling with the syntax - specifically how I can take my big SQL scripts (which are just a combination of INSERT INTO, UPDATE, CREATE, DROP, DELETE, etc statements) and throw them into a stored procedure with some very basic error handling.
What I'm hoping for is either:
a quick & dirty dummy's guide to taking my depressing blob of PL/SQL and get it to execute within a stored procedure OR
Any alternative (if a stored proc isn't appropriate) which offers the same functionality, ie. a way to execute a bunch of SQL statements and rollback if any of these statements throw an exception.
About my attempts - I've tried copying portions of my SQL scripts into a stored procedure but they always fail to compile with the error 'PLS-00103 Encountered the symbol when expecting one of the following'. eg.
CREATE OR REPLACE PROCEDURE ETL_2618A AS
BEGIN
DROP SEQUENCE "METER_REPORTING"."SEQ_2618";
CREATE SEQUENCE SEQ_2618;
END ETL_2618A;
Oracle documentation isn't terribly accessible and I've not had much luck with googling/searching StackOverflow, but I apologise if I've missed something obvious.
To do DDL in PL/SQL you need to use dynamic sql.
CREATE OR REPLACE PROCEDURE testProc IS
s_sql VARCHAR2(500);
BEGIN
s_sql := 'DROP SEQUENCE "METER_REPORTING"."SEQ_2618"';
EXECUTE IMMEDIATE s_sql;
s_sql := 'CREATE SEQUENCE "METER_REPORTING"."SEQ_2618"';
EXECUTE IMMEDIATE s_sql;
EXCEPTION
WHEN OTHERS THEN
NULL;
end testProc;
/
If you run the script in sqlplus you can use:
whenever sqlerror
to control what should happen when an error occurs.
http://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12052.htm
Adding exception handling to a PL/SQL proc or script isn't difficult, but of course some coding is required. Here's your procedure dressed up slightly with some very basic error reporting added:
CREATE OR REPLACE PROCEDURE ETL_2618A AS
nCheckpoint NUMBER;
BEGIN
nCheckpoint := 1;
EXECUTE IMMEDIATE 'DROP SEQUENCE "METER_REPORTING"."SEQ_2618"';
nCheckpoint := 2;
EXECUTE IMMEDIATE 'CREATE SEQUENCE SEQ_2618';
RETURN;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('ETL_2618A failed at checkpoint ' || nCheckpoint ||
' with error ' || SQLCODE || ' : ' || SQLERRM);
RAISE;
END ETL_2618A;
Not tested on animals - you'll be first! :-)