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Make the Most of PL/SQL Bulk Processing

The bulk processing features of PL/SQL (BULK COLLECT and FORALL) are key tools for improving performance of programs that currently rely on row-by-row processing, an example of which is shown below.

Use this blog post to quickly get to some of the best resources on bulk processing - from articles to quizzes to workouts to tutorials.
LiveSQL Tutorial I offer a 19-module tutorial on all things bulk processing here. I complement the explanations with lots of code to run and explore, along with:
Fill in the Blanks: partially-written code that you need to finish up, that reinforces the content of that moduleExercises: You do all the coding to solve the stated requirement (be on the lookout for copy/paste opportunities from the module to speed things up). Oracle-BASE Content You can always depend on Tim Hall to offer comprehensive coverage of SQL and PL/SQL features, with straightforward, easy-to-run code snippets to drive the points home. You'll find his coverage of bulk processing her…

How to make sure your code FAILS to compile

Huh, what?

Make sure my code fails to compile?

Why would I want to do that.

Well, suppose that you had a compute-intensive procedure that ran every hour and benefited greatly from full PL/SQL compiler optimization (level set to 3, to take advantage of subprogram inlining and everything else it does).

Next, suppose that somehow as the procedure (newly enhanced, fully tested) was being deployed to production, the optimization level was mistakenly set to 0 or 1. This would cause severe performance problems.

So in that case, wouldn't it be nice if you could build a "circuit breaker" into that procedure so that the compiler says "No go" even if the code itself compiles just fine?

I think it would be nice - and you can accomplish precisely that with the error directive of the conditional compilation feature of PL/SQL.

First, here's the code that demonstrates precisely the scenario outlined above.
CREATE OR REPLACE PROCEDURE compute_intensive AUTHID DEFINER IS BE…

Use RETURNING Clause to Avoid Unnecessary SQL Statements

The RETURNING clause allows you to retrieve values of columns (and expressions based on columns) that were modified by an insert, delete or update. Without RETURNING you would have to run a SELECT statement after the DML statement is completed, in order to obtain the values of the changed columns. So RETURNING helps avoid another roundtrip to the database, another context switch in a PL/SQL block.

The RETURNING clause can return multiple rows of data, in which case you will use the RETURNING BULK COLLECT INTO form.

You can also call aggregate functions in the RETURNING clause to obtain sums, counts and so on of columns in multiple rows changed by the DML statement.

Finally, you can also use RETURNING with EXECUTE IMMEDIATE (for dynamically constructed and executed SQL statements).

Run this LiveSQL script to see all of the statements shown below "in action."

First, I will create a table to use in my scripts:
CREATE TABLE parts ( part_number INTEGER , part_name VARCH…

Does the PL/SQL compiler remove code that is used?

Yes. No. Sort of.

 It's (not all that) complicated.

This question hit my Twitter feed yesterday:
When you enable all warnings, have you ever seen a "PLW-06006-- uncalled procedure removed" (lots of them), when they surely are called? Now that, I must admit, has to be a little bit concerning. You write code, you know it is going to, or should be, executed, and yet the PL/SQL compiler tells you it's been removed?

OK, OK, calm down. Everything is just fine.

Here's the explanation:
The optimizer performed an inlining optimization, so all the code for that procedure (or function) was moved to where it is invoked.The "original" nested or private subprogram that you wrote (and, don't worry, is still and always will be in the source code of your program unit) is, truth be told, never going to be called. So then the compiler removed it (did not include it in the compiled code - which is not PL/SQL code any longer). Let's take a look at some code, and what…

Setting and using your own conditional compilation flags

This post is the fourth in my series on conditional compilation. You will find links to the entire series at the bottom.

In this post, I explore how to set and use conditional compilation flags (also known as inquiry directives and referred to below as ccflags) used in $IF statements, and control which code will be included or excluded when compilation occurs.

In theory, you don't need ccflags at all. You could just create a package with static constants, like DBMS_DB_VERSION, and then reference those constants in $IF statements. That makes sense when many different compilation units (packages, procedures, triggers, functions, object types) need to be consistently controlled by the same settings. With the package approach, when you change a value for the constant, the dependent program units will be invalidated, and upon recompilation, will be compiled with the new values.

If, on the other hand, you want to add conditional compilation logic to a single unit, or a handful, then yo…

Writing code to support multiple versions of Oracle Database

3rd in a series on conditional compilation. See end of post for links to all posts in the series.

Do you write code that must run on more than one version of Oracle Database? This is almost always the case for suppliers of "off the shelf" applications. And when confronted with this reality, most developers choose between these two options:

Use only those features available in all versions ("lowest common denominator" or LCD programming).
or Maintain separate copies of the code for each supported version, so you can take advantage of new features in later versions of the database ("sure to create a mess" or SCAM programming).

And let's face it, both have some serious drawbacks.

The LCD approach ensures that your code will compile on all supported versions. But you will sacrifice the ability to take advantage of new features in the later versions. That can be a high price to pay.

The SCAM approach, well, "sure to create a mess" says it all. Wh…

Nine Years at the Oracle Dev Gym

Waaaaay back in 2010, on April 8 to be specific, I started a website called the PL/SQL Challenge. It featured a daily PL/SQL quiz (yes, that's right - a new quiz every weekday!) and gave Oracle Database developers a way to both deepen and demonstrate their expertise. Players were ranked and competed for top honors in our annual championships.

Not quite as waaaaay back, in 2014, I rejoined Oracle Corporation after 22 years away (from the company, not from the technology). The PL/SQL Challenge came with me, and a year later we rebranded it as the Oracle Dev Gym.

Today, we offer quizzes on SQL, PL/SQL, database design, logic, Java and Application Express. We've added workouts and classes.

Yesterday we celebrated the ninth anniversary of the Dev Gym / PL/SQL Challenge. And my oh my but Oracle Database developers have been busy!


Here are some stats from those nine years: Almost 35,000 developers and DBAs have taken quizzes on the site, a total of 1.27M answers submitted.They spent a…

Viewing conditionally compiled code: what will be run?

2nd in a series on conditional compilation. See end of post for links to all posts in the series.

In the previous (first) post in my series on conditional compilation, I covered use cases and presented some simple examples.

In this post, I show you how you can confirm what code is actually going to be executed after compilation. Without conditional compilation, this is of course a silly exercise. The code that is executed is the same as the code you see in your editor.

But with conditional compilation, the code that is compiled and therefore runs could depend on any of the following:
The version of the database in which it is compiledThe values of user-defined conditional compilation flagsThe values of pre-defined (system) conditional compilation flags, like ##plsq1_optimize_level It can be a little bit nerve-wracking for a developer to not be entirely sure what is going to execute, so we provide the DBMS_PREPROCESSOR package, with its two subprograms: print_post_processed_source - disp…

One exception handler for all packaged subprograms?

This question was submitted as a comment in one of my videos today:
Do we have to include an exception section for each individual subprogram or can we have a single handler for all subprograms? The quick answer is: if you want an exception raised in a procedure or function defined in a package, you need to add an exception to that subprogram.

I can certainly see why this question would come up. A package body can have its own exception handler. Here's an example:
CREATE OR REPLACE PACKAGE pkg AUTHID DEFINER IS PROCEDURE proc; END; / CREATE OR REPLACE PACKAGE BODY pkg IS PROCEDURE proc IS BEGIN RAISE NO_DATA_FOUND; END; BEGIN NULL; EXCEPTION WHEN NO_DATA_FOUND THEN DBMS_OUTPUT.put_line ('Was proc executed?'); END; / And it kinda, sorta looks like if I execute the following block, I will see "Was proc executed?" on my screen.
BEGIN pkg.proc; END; / But I would be wrong. Instead, I will see:
ORA-01403: no data found ORA-0651…

European Union Mandates All Business Logic in Database by 2020

DatelineDB: April 1st 2019

The European Union turned heads today with a surprise announcement:
Starting 1 January 2020, all business logic in applications must be made available via code stored inside the database. While we recommend that you use Oracle Database and PL/SQL, that will not be required. This position was apparently taken after close review of the groundbreaking research conducted by Toon Koppelaars of Oracle Corporation, in which he showed that by putting business logic in the database, the overall work - and therefore energy consumption - of the application is reduced, sometimes by as much as 235%. While improving the overall performance of the application by 500%.

A close confidant of the President of the European Union told DatelineDB that the EU would soon adopt a resolution stating that we are now in a climate emergency and every effort must be made in every aspect of human activity to slow down the warming of our planet.

"So the decision to require business lo…

An introduction to conditional compilation

1st in a series on conditional compilation. See end of post for links to all posts in the series.

Conditional compilation allows the compiler to compile selected parts of a program based on conditions you specify using $ syntax in PL/SQL. When you see statements like $IF, $ELSE, $END and $ERROR in your PL/SQL code, you are looking at conditional compilations, sometimes also referred to as "ifdef" processing.

There's a really good chance you've never taken advantage of conditional compilation in PL/SQL, so I thought I'd write up a few blog posts about why you might want to use it - and then how to put it to use.

Conditional compilation comes in very handy when you need to do any of the following:
Compile and run your PL/SQL code base on different versions of Oracle, taking advantage of features specific to those versions. Run certain code during testing and debugging, but then omit that code from the production code. Or vice versa. Install/compile different elements…

Results of the Oracle Dev Gym PL/SQL Challenge Championship for 2018

You will find below the rankings for the PL/SQL Challenge Championship for quizzes taken in 2018. The number next to the player's name is the number of times that player has participated in a championship. Below the table of results for this championship, you will find another list showing the championship history of each of these players.

Congratulations first and foremost to our top-ranked players:

1st Place: mentzel.iudith
2nd Place: Andrey Zaytsev
3rd Place: Tony Winn


Next, congratulations to everyone who played in the championship. We hope you found it entertaining, challenging and educational. And for those who were not able to participate in the championship, you can take the quizzes through the Practice feature. We will also make the championship as a whole available as a Test, so you can take it just like these players did.

Finally, many thanks and our deepest gratitude to our reviewers, especially Elic, who has once again performed an invaluable service to our community.

R…

Using sparse collections with FORALL

FORALL is a key performance feature of PL/SQL. It helps you avoid row-by-row processing of non-query DML (insert, update, delete, merge) from within a PL/QL block. Best of all, almost always, is to do all your processing entirely within a single SQL statement. Sometimes, however, that isn't possible (for example, you need to sidestep SQL's "all or nothing" approach) or simply too difficult (not all of us have the insane SQL writing skills of a Tom Kyte or a Chris Saxon or a Connor McDonald).

To dive in deep on FORALL, check out any of the following resources:
FORALL documentationVideos at Practically Perfect PL/SQL Tim Hall on Bulk Binds In this post, I am going to focus on special features of FORALL that make it easy to work with space collections: the INDICES OF and VALUES OF clauses.

Typical FORALL Usage with Dense Bind Array

Here's the format you will most commonly see with FORALL: the header looks just like a numeric FOR loop, but notice: no loop keywords. Two…