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. Just don't reference them...

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

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

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

    ReplyDelete
  7. 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. 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. 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

Quick Guide to User-Defined Types in Oracle PL/SQL

A Twitter follower recently asked for more information on user-defined types in the PL/SQL language, and I figured the best way to answer is to offer up this blog post. PL/SQL is a strongly-typed language . Before you can work with a variable or constant, it must be declared with a type (yes, PL/SQL also supports lots of implicit conversions from one type to another, but still, everything must be declared with a type). PL/SQL offers a wide array of pre-defined data types , both in the language natively (such as VARCHAR2, PLS_INTEGER, BOOLEAN, etc.) and in a variety of supplied packages (e.g., the NUMBER_TABLE collection type in the DBMS_SQL package). Data types in PL/SQL can be scalars, such as strings and numbers, or composite (consisting of one or more scalars), such as record types, collection types and object types. You can't really declare your own "user-defined" scalars, though you can define subtypes  from those scalars, which can be very helpful from the p

The differences between deterministic and result cache features

 EVERY once in a while, a developer gets in touch with a question like this: I am confused about the exact difference between deterministic and result_cache. Do they have different application use cases? I have used deterministic feature in many functions which retrieve data from some lookup tables. Is it essential to replace these 'deterministic' key words with 'result_cache'?  So I thought I'd write a post about the differences between these two features. But first, let's make sure we all understand what it means for a function to be  deterministic. From Wikipedia : In computer science, a deterministic algorithm is an algorithm which, given a particular input, will always produce the same output, with the underlying machine always passing through the same sequence of states.  Another way of putting this is that a deterministic subprogram (procedure or function) has no side-effects. If you pass a certain set of arguments for the parameters, you will always get

My two favorite APEX 5 features: Regional Display Selector and Cards

We (the over-sized development team for the PL/SQL Challenge - myself and my son, Eli) have been busy creating a new website on top of the PLCH platform (tables and packages): The Oracle Dev Gym! In a few short months (and just a part time involvement by yours truly), we have leveraged Oracle Application Express 5 to create what I think is an elegant, easy-to-use site that our users will absolutely love.  We plan to initially make the Dev Gym available only for current users of PL/SQL Challenge, so we can get feedback from our loyal user base. We will make the necessary adjustments and then offer it for general availability later this year. Anyway, more on that as the date approaches (the date being June 27, the APEX Open Mic Night at Kscope16 , where I will present it to a packed room of APEX experts). What I want to talk about today are two features of APEX that are making me so happy these days: Regional Display Selector and Cards. Regional Display Sel