Skip to main content

PL/SQL Brain Teaser: compile procedure with two declarations with same name?

I posted my second PL/SQL brain teaser on Twitter today @sfonplsql:

I can compile a procedure successfully even tho it contains two declarations with the same name for the identifier. Can you?

 But Twitter is probably not the best way to do this, since it is not easy to capture every nuance in a tweet.

 For example, Jonathan Whitehead asked: "Complier directives?"

Which leads me to "tweak" the brain teaser to fully elaborate as follows:

 The Brain Teaser

 I can compile a procedure successfully even though it contains two declarations with the same name for the identifier. And after compilation, if I run DBMS_PREPROCESSOR.print_post_processed_source to display the actual source code that was compiled into the database, it will show BOTH of those declarations.

 OK....now, clever PL/SQL developers, can you post an example of code that will solve this teaser?

Comments

  1. Oren Nakdimon (@DBoriented)April 9, 2015 at 10:13 AM

    Just don't reference them...

    CREATE OR REPLACE PROCEDURE p AS
    x NUMBER;
    x NUMBER;
    y NUMBER;
    BEGIN
    y := 5;
    END p;
    /

    ReplyDelete
  2. Steven FeuersteinApril 9, 2015 at 10:19 AM

    Nice work, Oren. Yes, that is the solution! It turns out that the PL/SQL compiler will not complain about two declarations with the same name - as long as you do not reference them in your code.

    ReplyDelete
  3. Atul GuptaApril 10, 2015 at 4:39 AM

    CREATE OR REPLACE PROCEDURE p AS
    x NUMBER := 8;
    x NUMBER := 9;
    y NUMBER;
    BEGIN
    DEClARE
    x NUMBER;
    BEGIN
    x := 6;
    END;
    END p;
    /

    ReplyDelete
  4. Steven FeuersteinApril 10, 2015 at 8:20 AM

    A pleasantly confusing variation on Oren's work. Nice, Atul.

    ReplyDelete
  5. Atul GuptaApril 10, 2015 at 8:45 AM

    Thanks Steven....

    How about


    CREATE OR REPLACE PROCEDURE p AS
    x NUMBER := -88888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888889999999999999999999999999999999999999988;
    x NUMBER := 9;
    y NUMBER;
    BEGIN
    DEClARE
    x NUMBER;
    BEGIN
    x := 6;
    END;
    END p;
    /

    It gives error numeric overflow or underflow.......

    looks like Oracle Checks initial assignment

    ReplyDelete
  6. Steven FeuersteinApril 10, 2015 at 8:48 AM

    Yes, an assignment of a default value would certainly count as a usage of that variable.

    ReplyDelete
  7. Atul GuptaApril 10, 2015 at 8:53 AM

    Steven One more

    CREATE OR REPLACE PROCEDURE p AS
    x NUMBER := -9999999999999988;
    x NUMBER := abs(-9) * 0;
    y NUMBER;
    BEGIN
    DEClARE
    x NUMBER;
    BEGIN
    x := 6;
    END;
    END p;
    /

    It complies OK.

    ReplyDelete
  8. Steven FeuersteinApril 10, 2015 at 8:56 AM

    Well you know what means? I was wrong! :-)

    And that's what happens when you state things about code without actually verifying them. Thanks, Atul!

    ReplyDelete
  9. iudithApril 10, 2015 at 10:01 AM

    Hello Steven, All,
    I think that it is a compiler bug that it does allow the duplicate declaration in the first place.
    Steven, unrelated to this issue, I would thank you in advance if you can look into
    a feedback that I just posted on the plsqlchallenge site ... I know that you don't have access to e-mail ...
    Thanks a lot & Best Regards,
    Iudith

    ReplyDelete

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