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. :-)