So which error is raised in 24 December quiz? (1805)

The 24 December quiz tested your knowledge of what happens when a CASE statement does not contain an ELSE clause and at runtime, none of the WHEN clauses are executed. The answer is that Oracle raises the "ORA-06592: CASE not found while executing CASE statement" error.

Several players wrote, however, to note that the local variable, l_text, is declared as VARCHAR2(20). So this assignment:

the_text := 'Santa is coming (for some, sort of, maybe)';

will raise a VALUE_ERROR exception. In other words, they chose the correct answer, but for the wrong reasons.

It is true that if statement assignment was executed, VALUE_ERROR would be raised and the text "Today is the 24th" would be displayed on the screen.

But that statement is never executed because of the lack of an ELSE clause.

I did not intend to introduce this issue into the quiz; the original quiz submitted by Michael used just "Santa is coming". But I "softened" the text - after all, many do not celebrate, do not believe in Santa, etc. - and neglected to increase the size of the string.

I will correct this in the question text. There will be no re-scoring of quiz answers.

Merry Christmas to those who celebrate,
Steven

Is a CLOB a string? A question raised about the 22 December quiz (1803)

The 22 December quiz tested your knowledge of the capabilities of both EXECUTE IMMEDIATE and DBMS_SQL to parse very long strings. We scored the following statement as incorrect:

"You cannot execute a string of more than 32,767 bytes as a dynamic SQL statement."

Oracle offers various mechanisms, especially in Oracle11g to bypass this limitation (the maximum size, that is, of a VARCHAR2 variable or literal).

One player emailed the following concern:

One of the choices for today's quiz looks somewhat ambiguous, namely the choice that says: "You cannot execute a string of more than 32,767 bytes as a dynamic SQL statement". If we take this literally as it is worded, then we could object that there is no such thing at all as a "string of more than 32,767 bytes", because this is the maximum length allowed to a VARCHAR2 string. If so, then this choice is supposed to be marked as correct. On the other hand, if string means "anything that is character data", including a CLOB, then this choice (though apparently in need to be marked as incorrect) falls over 2 other choices, namely: a) the choice that says "You can use a subprogram of the DBMS_SQL package to parse a SQL statement whose length exceeds 32767 bytes ( by the way, the wording of this choice ellegantly avoids speaking of a "string whose length exceeds 32767, but speaks of a STATEMENT whose lengths exceeds 32767, thus avoiding the above problem). and b) the choice that says "In Oracle11g you can pass a CLOB to EXECUTE IMMEDIATE. These 2 choices in fact do cover in entirety the 2 cases of using a statement contents as a CLOB. I think that the wording of the choice that says "You can use a subprogram of the DBMS_SQL package to parse a SQL statement whose length exceeds 32767 bytes" is excellent, covering (even without specifying it explicitly) ALL the cases by which a statemnent longer than 32767 can be made "to fit into" the requirements of DBMS_SQL, be it by using a CLOB or by "breaking" the statement's contents into elements of a DBMS_SQL.VARCHAR2A array. So, in my opinion, the problematic choice recommends itself to be rescored due to the ambiguous wording.

The SQL Language Reference says the following about CLOBs: "The CLOB data type stores single-byte and multibyte character data." CLOBs are, therefore, character data, which is another general term for string. VARCHAR2s are also character data, with a maximum length of 32767. But I believe that it is correct to interpret string as a general category of data including CHAR, VARCHAR2, NCHAR, NVARCHAR, CLOB and NCLOB (any others?). Others also feel this way; see:  http://www.orafaq.com/forum/t/98334/2/.

You are correct that two other choices covered the correct descriptions of ways to parse very long strings. I do not see, however, what bearing that fact has on the other choice, which is incorrect.

So I do not see the need to rescore. What do you think?

Release 1.8 of PL/SQL Challenge in Production

We have successfully upgraded PL/SQL Challenge to release 1.8, which includes these significant new features and changes:

* Remember Me: a long-requested enhancement, you can check the "Remember me" box before you login. We will then automatically log you in to the PL/SQL Challenge on subsequent visits to the website. If you do not visit the site for seven days, you will be prompted to login again.

* Public Profile: you can now record much more information about yourself and your career as a PL/SQL developer. This information is then made available on a public player profile page - but only if you explicitly approve the publication of that content. All player names on the site are hyperlinked to this page. We also provide you with a public URL so that this profile can be accessed from outside of the PL/SQL Challenge website (such as from your blog).

* Streamlined "Take the Quiz" process: You no longer have to scroll down through assumptions and advice. You can choose to view the information or simply press the Play Now button to get right to the quiz.

* Post-Quiz Survey and Player Notes: after you take the quiz, we now invite you to provide us with feedback on the quality of the quiz. You can also record notes regarding that quiz for future reference. The notes will appear on the Past Quiz page. You can also take the survey at any time after you take the quiz.

* Submit Your Own Quiz Idea: you can now submit your own idea for a quiz directly from the website, both from the "Submit Quiz Idea" on the home page and from several other places on the site as well. If your quiz is accepted, your name will be posted the day the quiz is taken. Get creative and share your expertise with us and players from around the world!

* Reorganization of Rules and Assumptions: the Rules page is gone, long live the Rules page! Most of the content of that page is now available in the FAQ. In addition, rules, assumptions and advice for the quiz is provided on the Take the Quiz page.


Warm regards and happy holidays,
Steven Feuerstein

Beta Test of Release 1.8 from 13 December to 17 December

We invite all PL/SQL Challenge players to visit test.plsqlchallenge.com and help us test the beta release of PL/SQL Challenge 1.8. You can log in at this site using your usual email/password combo. The quizzes shown for this week are from the first week of the PL/SQL Challenge. All past quiz data should be available to you for ranking and reporting.

This version of the PL/SQL Challenge includes these significant new features:

* Remember Me: a long-requested enhancement, you can check the "Remember me" box before you login. We will then automatically log you in to the PL/SQL Challenge on subsequent visits to the website. If you do not visit the site for seven days, you will be prompted to login again.

* Public Profile: you can now record much more information about yourself and your career as a PL/SQL developer. This information is then made available on a public player profile page - but only if you explicitly approve the publication of that content. All player names on the site are hyperlinked to this page. We also provide you with a public URL so that this profile can be accessed from outside of the PL/SQL Challenge website (such as from your blog).

* Streamlined "Take the Quiz" process: You no longer have to scroll down through assumptions and advice. You can choose to view the information or simply press the Play Now button to get right to the quiz.

* Post-Quiz Survey and Player Notes: after you take the quiz, we now invite you to provide us with feedback on the quality of the quiz. You can also record notes regarding that quiz for future reference. The notes will appear on the Past Quiz page. You can also take the survey at any time after you take the quiz.

* Submit Your Own Quiz Idea: you can now submit your own idea for a quiz directly from the website, both from the "Submit Quiz Idea" on the home page and from several other places on the site as well. If your quiz is accepted, your name will be posted the day the quiz is taken. Get creative and share your expertise with us and players from around the world!

* Reorganization of Rules and Assumptions: the Rules page is gone, long live the Rules page! Most of the content of that page is now available in the FAQ. In addition, rules, assumptions and advice for the quiz is provided on the Take the Quiz page.

Lots of great stuff, I hope you will agree! Now we need your help this week to uncover bugs and fine tune the flow on the website. If you have a few spare moments, please play around with setting up a comprehensive player profile. Are we missing any critical information you'd like to record about your career as a PL/SQL developer? And take the quiz survey. Are the questions asked appropriate to your experience with the quiz and the kind of feedback you'd like to provide?

Thanks in advance for your assistance and remember: any data entered during the beta test will NOT be carried over to production.

Many thanks in advance,
Steven Feuerstein

Every block will fail with an error? Not so, say players. (1764)

In the 9 December quiz, I test your knowledge of subprogram overloading and the problem of ambiguous overloading. One choice, marked as correct, stated: "Any block of code that includes a call to salespkg.calc_total will result in Oracle raising an error when executed." I received two objections to this statement: 1. What if, a player asked, my block looked like this:

BEGIN
   IF 1 = 2
   THEN
      EXECUTE IMMEDIATE 'call salespkg.calc_total(''A'')';
   END IF;
END;

Then this block will not raise an error, even though it "calls" the program. 2. "I do not agree with the answer "Any block of code that includes a call to salespkg.calc_total will result in Oracle raising an error when executed", especially the words "any" and "when executed". Of course, an anonymous block will give a runtime error. But when I include this call in a procedure or package (a "block of code" as well), I will never be able to execute this, because it won't even compile (PLS-00307)! So, in this case, the block of code will NEVER result in an Oracle (runtime) error, because it will never be executed. Because of that, I scored this answer as incorrect" Here is my response: 1. Well, look at that! A player found a "hole" in my statement. I said "includes a call" but I never said that the block had to actually execute the subprogram. Further, he hides the call to the ambiguously overloaded subprogram inside a dynamic PL/SQL block so that the static block with compile. Very ingenious - and irritating. :-) It is so ingenious, in fact, that I am entirely loath to rescore everyone's answers as correct on this point. I will grant that I had a "hole" in my statement and fix that in the text. I will give this player credit for a correct answer on this statement - and I will do so for anyone else who chose "incorrect" for this option because of this - you will need to submit a request through Feedback on the website. Finally, this player (_Nikotin) will receive an O'Reilly Media ebook as a reward for finding a way to maneuver around the language of this statement. 2. I do not agree with this objection. The bottom line is that you cannot execute a block that contains a call to (and that executes) any of these subprograms. Either you cannot run that block because it fails to compile due to an ambiguous overloading or because it is calling a subprogram that is invalid (due to an ambiguous overloading). Either way, you cannot execute that block. Your thoughts?

Questions regarding quiz on object types (7 December quiz) (1762)

A player wrote the following: Hello Steven, Just a few remarks regarding the last quiz, that I would like to hear your opinion on: 1. Regarding the creation on an object type containing STATIC subprograms only, without any attributes: While it is right that such a type is practically substitutable with a PL/SQL package, as far as I know, in Java this is allowed. Since the object oriented features in Oracle usually attempt "to mimic" the constructs and behavior of other object oriented languages, I don't see any reason for such a construct not being allowed in Oracle as well, at least technically, even if practically it is of course of a limited use. The only limitation might be that such a type should be NOT INSTANTIABLE (and therefore not storable in a database column, a.s.o.). In fact, maybe it might contain MEMBER procedures also and still being without attributes. 2. Regarding the restriction that the methods declarations should always come after the type's attributes: I think that this is also a superfluous restriction. While the order of the attributes is essential, just like the order of the columns in a table, for example for clearly determining the order of the arguments in calling the type's constructor, the order of the methods declarations seems to be not relevant and they can probably come as well in any position inside the type definition, similar to the order of subprograms in a package. This would be more similar to Oracle's general behavior of allowing independent clauses in any CREATE statement to come in any order in most cases. As a quick example, in a table definition you can put constraints before column definitions, like in the following: create table mytab (constraint mytab_pk primary key (x), x number not null); It is true that a reasonable person will probably NOT code things like this, and NONE of the examples in the different documentation sources will ever use such an awkward syntax, but this means that you have practically only 2 ways of knowing that this DOES NOT work: a. either to have tried it out by yourself (which probably nobody did, well ... at least until this quiz ... ) or b. to closely follow-up the complete railroad syntax diagram. I am not sure whether this restriction is explicitely mentioned in the documentation. I would love to read your opinion on these issues. I am quite busy at the moment and do not have time to respond, so I thought I would post this for others to consider. Regards, Steven

Misleading terminology in 8 December quiz on varrays? (1763)

The quiz tested your knowlege of the ability to adjust at runtime the maximum number of elements allowed in a varray. One player felt my use of the phrase "upper bound" was ambiguous: 'In todays question we have a problem about term upper bound, because there's a difference between upper bound and maximum size, as pointed in Oracle Documentation as "A varray has a maximum size, which you specify in its type definition. Its index has a fixed lower bound of 1 and an extensible upper bound." (PL/SQL User Guide, Understanding Varrays) So in some choices we can understand which variant of that two is meant, for example in choices … can only be changed… and … using the ALTER TYPE… almost obviously upper bound means maximum size. But in other cases meaning of "upper bound" is not so clear.' To which I reply: an interesting point, but I think that there is no ambiguity in the context of this question, which states: "The varray is one of three types of collections in PL/SQL, and it is the only kind of collection for which you specify an upper bound on the number of elements that can be placed in the collection variable declared on a varray type." In other words, I clearly define "upper bound" as referring to the number of elements. So I do not see that there is any reason to change the scoring of the quiz for this reason. A couple of other players expressed concern about my scoring as correct the statement "You can change the upper bound of a varray from within a PL/SQL block." Here is the most detailed explanation: "I think that one of the choices of today's quiz is a little bit ambiguous, namely the choice that says: "You can change the upper bound of a varray from within a PL/SQL block". The ambiguity is that, if we consider the EXECUTE IMMEDIATE statement, then ANYTHING that can be done at all out of a PL/SQL block can also be done inside a PL/SQL block, be it changing a varray's upper bound or any other DDL operation and even beyond ... The "flavor of the whole question" rather suggests that this WAS NOT the expected way of thinking, otherwise this choice "fails back" to the other one, that speaks about ALTER TYPE. Instead, I think that the intention was more probably to underline that the effective upper bound of a varray variable declared in a PL/SQL block cannot be changed beyond the defined upper bound of the SQL type by using pure PL/SQL statements, like for example l_var.EXTEND, a.s.o. I feel that some different wording of this choice would have been welcome, maybe something like "If L_ARR is a pl/sql variable of a varray type then L_ARR.limit cannot be changed in a PL/SQL block". Am I wrong ? I wonder what others will think of this." To which I reply: watch out for reading too much into the choices. If faced with a choice between trying to deduce the "flavor" of the question and accepting what the choice says "as is", you should always go with the latter approach. I really had in mind nothing more than the fact that you can use EXECUTE IMMEDIATE to also change the limit of the varray type from within a PL/SQL block. Look on the bright side: if you are comfortable enough with Oracle and PL/SQL to know that "anything" can be done in a PL/SQL block with EXECUTE IMMEDIATE, then you can quickly check all such choices as correct in future quizzes! Cheers, Steven