Skip to main content

PL/SQL Puzzle: Getting the "right" error message to appear

I posted the following puzzle on Twitter:
What change(s) can you make to this code so that "ORA-00001: unique constraint" appears on the screen after execution?
Try it yourself before reading the rest of the post!


White space


so you do not immediately


see my answer. 


:-)

Here are the answers from the TwitterSphere:

Change line 5's assignment to dbms_sql.number_table(1=>1,2=>1)

In other words, try to insert the same value twice. Since there is a unique index on the column, that will cause ORA-00001 to be raised.

So that will do it, right?

Wrong. Hans and Dirk both point out why that is not enough, and offer the second part of the solution:

The value deposited in the error_code field of the SQL%BULK_EXCEPTIONS array is unsigned. In other words, 1 rather than -1 is stored. Unfortunately, the SQLERRM function assumes that the error code you pass it will be signed (negatively). So you must multiply the value in the pseudo-collection by -1. Then SQLERRM will return the right string.

Or as Dirk puts it:

(sqlerrm (sql%bulk_exceptions (indx).error_code));

must be

(sqlerrm (0 - sql%bulk_exceptions (indx).error_code));

You don't really need the 0, though. You can write simply:

(sqlerrm (-sql%bulk_exceptions (indx).error_code));

You can see all these variations at work in my LiveSQL script.

Actually, I was surprised that I did not receive any "silly" answers. After all, there are lots of ways to get "ORA-00001: unique constraint" to appear on the screen, such as:

DECLARE 
   two_ts DBMS_SQL.number_table := DBMS_SQL.number_table (1=>1,2=>2); 
BEGIN 
   DBMS_OUTPUT.PUT_LINE ('ORA-00001: unique constraint');
   RETURN;
   
   FORALL indx IN 1 .. 2 
   SAVE EXCEPTIONS 
      INSERT INTO t VALUES (two_ts(indx)); 
   DBMS_OUTPUT.put_line (SQL%ROWCOUNT || ' inserted'); 
   ROLLBACK; 
EXCEPTION 
   WHEN others 
   THEN 
      FOR indx IN 1 .. SQL%BULK_EXCEPTIONS.COUNT 
      LOOP 
         DBMS_OUTPUT.put_line 
            (SQLERRM (SQL%BULK_EXCEPTIONS (indx).ERROR_CODE)); 
      END LOOP; 
END;

Yes, that's right, simply display it on the screen and then shortcut everything else with RETURN; (or not, let the rest of the code execute unchanged).

I guess it was a serious week for the Oracle Database developer community. :-)
Labels:

Comments

Post a Comment

Popular posts from this blog

Running out of PGA memory with MULTISET ops? Watch out for DISTINCT!

A PL/SQL team inside Oracle made excellent use of nested tables and MULTISET operators in SQL, blending data in tables with procedurally-generated datasets (nested tables).  All was going well when they hit the dreaded: ORA-04030: out of process memory when trying to allocate 2032 bytes  They asked for my help.  The error occurred on this SELECT: SELECT  *    FROM header_tab trx    WHERE (generated_ntab1 SUBMULTISET OF trx.column_ntab)       AND ((trx.column_ntab MULTISET             EXCEPT DISTINCT generated_ntab2) IS EMPTY) The problem is clearly related to the use of those nested tables. Now, there was clearly sufficient PGA for the nested tables themselves. So the problem was in executing the MULTISET-related functionality. We talked for a bit about dropping the use of nested tables and instead doing everything in SQL, to avoid the PGA error. That would, however require lots of wo...
4 comments
Read more

How to Pick the Limit for BULK COLLECT

This question rolled into my In Box today: In the case of using the LIMIT clause of BULK COLLECT, how do we decide what value to use for the limit? First I give the quick answer, then I provide support for that answer Quick Answer Start with 100. That's the default (and only) setting for cursor FOR loop optimizations. It offers a sweet spot of improved performance over row-by-row and not-too-much PGA memory consumption. Test to see if that's fast enough (likely will be for many cases). If not, try higher values until you reach the performance level you need - and you are not consuming too much PGA memory.  Don't hard-code the limit value: make it a parameter to your subprogram or a constant in a package specification. Don't put anything in the collection you don't need. [from Giulio Dottorini] Remember: each session that runs this code will use that amount of memory. Background When you use BULK COLLECT, you retrieve more than row with each fetch, ...
4 comments
Read more

PL/SQL 101: Three ways to get error message/stack in PL/SQL

The PL/SQL Challenge quiz for 10 September - 16 September 2016 explored the different ways you can obtain the error message / stack in PL/SQL. Note: an error stack is a sequence of multiple error messages that can occur when an exception is propagated and re-raised through several layers of nested blocks. The three ways are: SQLERRM - The original, traditional and (oddly enough) not currently recommended function to get the current error message. Not recommended because the next two options avoid a problem which you are unlikely  to run into: the error stack will be truncated at 512 bytes, and you might lose some error information. DBMS_UTILITY.FORMAT_ERROR_STACK - Returns the error message / stack, and will not truncate your string like SQLERRM will. UTL_CALL_STACK API - Added in Oracle Database 12c, the UTL_CALL_STACK package offers a comprehensive API into the execution call stack, the error stack and the error backtrace.  Note: check out this LiveSQL script if...
5 comments
Read more