Rounding amounts, divide cents over multiple lines

In previous articles I wrote about dealing with a missing cent when you need to divide a certain amount over multiple lines. In these articles, links are at the bottom, I described a method to calculate the difference on the last row.
Then a question arose (as a comment):
What if for example i have 42 records and i wish to divide 100 by 42. I would get a rounded value of 2.38. If (more...)

Debug PL/SQL Web Pages

What happens when you can’t get a PL/SQL Web Toolkit to work because it only prints to a web page? That’s more tedious because any dbms_output.put_line command you embed only prints to a SQL*Plus session. The answer is quite simple, you create a test case and test it inside a SQL*Plus environment.

Here’s a sample web page that fails to run successfully …


Subtleties – Part 2 (Nested Tables and Varrays)

In Part 1 we saw that the SQL function COLLECT with the DISTINCT option is not natively supported in PL/SQL.
One suggested workaround was to apply the SET function on the result of the “simple” COLLECT function (without the DISTINCT option).
This works fine, in both SQL and PL/SQL, as long as the collection type that we use is Nested Table.

create type integer_ntt as table of integer

select person_id,set(cast(collect(project_id) as integer_ntt)) project_id_list

Subtleties – Part 1 (SQL and PL/SQL)

Almost every valid SQL statement (i.e., that is executed successfully by the SQL engine) can be embedded successfully as a static SQL in PL/SQL. Almost, but not every statement.
One example is the COLLECT aggregate function with the DISTINCT option.

To demonstrate it I’ll use the PROJECT_ASSIGNMENTS table, which contains assignments of people to projects. The same person may be assigned to the same project more than once, in different times.

create table  (more...)

Continuous Delivery and the Oracle database (III)

In this series of blogs about Continuous Delivery and the Oracle database, I describe how to automate deployments (installations). In the previous two Blogs I have described the tools and techniques used to create and install migration scripts.

In this Blog I will describe the ‘(un)happy flow’ for a database deployment: what to do if the deployment (installation) is correct (the ‘happy flow’) and what to do if it goes wrong (the ‘unhappy flow’)?


Improving PL/SQL performance in APEX

One of the simplest tuning techniques to encapsulate PL/SQL used in APEX within packages, minimising the size of anonymous blocks. This applies to any PL/SQL within the page, including computations, processes, plugins, dynamic actions, validations, shortcuts and dynamic PL/SQL regions.

This change can make a big impact in the execution time of PL/SQL as it's processed at compile time instead of interpreted at runtime.

Plug-ins can be wonderful black boxes and consumers may not care (more...)

The importance of cohesion

"Come on, come on, let's stick together" - Bryan Ferry

There's more to PL/SQL programs than packages, but most of our code will live in packages. The PL/SQL Reference offers the following benefits of organising our code into packages:

Modularity - we encapsulate logically related components into an easy to understand structure.

Easier Application Design - we can start with the interface in the package specification and code the implementation later.

Hidden Implementation (more...)

Parse JSON Array in SQL and PL/SQL – turn to a Nested Table

Transferring data between technologies and application tiers is done using various formats – binary, native on the one hand and open, text based such as CSV, XML and JSON on the other. Use of JSON is rapidly growing as a growing number of platforms and technologies provides support for JSON.

I recently was working on a Node.js application that exposed a REST API to HTTP consumers. The consumers could send POST requests with a (more...)

Email made Easier

an e-mail letter that has a @ sign on itSending emails from the Oracle database can be both simply deceptively braindead easy, and confoundingly perplexingly awful at the same time. Easy, because all you have to do is call one of the supplied mail packages to send an email:

  (sender     => ''
  ,recipients => ''
  ,subject    => 'Test Subject'
  ,message    => 'Test Message');
  (p_from => ''
  ,p_to   => ''
  ,p_subj => 'Test Subject'
  ,p_body => 'Test Message'

If (more...)

Blog Continuous Delivery and the Oracle database (II)

In the previous Blog I have described how to implement CD for an Oracle database by using migration scripts.

In this Blog I will describe how to create migration scripts (automagically).

DML scripts
This is the more simple case because you need them less often. There are various data compare tools which create scripts to migrate the differences between a source and target schema:
dbForge Data Compare for Oracle, v3.7 Express (free)

STRING_SPLIT im SQL Server 2016

Vor einiger Zeit habe ich in der Sektion database ideas bei OTN folgenden Wunsch geäußert: a string splitting function like SPLIT_PART in postgres. SPLIT_PART erhält als Argumente einen String und einen Delimiter, zerlegt den String an den Positionen der Delimiter-Zeichen in Substrings und liefert den n-ten Teilstring:


Das ist sicherlich keine höhere Magie und kann in SQL auf verschiedenen Wegen erreicht werden (etwa durch den Einsatz regulärer Ausdrücke), (more...)

Gear up for #AIOUG OTN Yathra’ 2016

Guys, AIOUG is back again with OTN Yathra’ 2016. It is a series of technology evangelist events organized by All India Oracle Users Group in six cities touring across the length and breadth of the country. It was my extreme pleasure to be the part of it in 2015 and I’m pleased to announce that … Continue reading

Working with the Interface Segregation Principle

Obviously Interface Segregation is crucial for implementing restricted access. For any given set of data there are three broad categories of access:

  • reporting 
  • manipulation 
  • administration and governance 

So we need to define at least one interface - packages - for each category in order that we can grant the appropriate access to different groups of users: read-only users, regular users, power users.

But there's more to Interface Segregation. This example is based on a procedure (more...)

Three more principles

Here are some more principles which can help us design better programs. These principles aren't part of an organized theory, and they're aren't particularly related to any programming paradigm. But each is part of the canon, and each is about the relationship between a program's interface and its implementation.

The Principle Of Least Astonishment

Also known as the Principle of Least Surprise, the rule is simple: programs should do what we expect them to (more...)

It’s all about the interface

When we talk about program design we're mainly talking about interface design. The interface is the part of our program that the users interact with. Normally discussion of UI focuses on GUI or UX, that is, the interface with the end user of our application.

But developers are users too.

Another developer writing a program which calls a routine in my program is a user of my code (and, I must remember, six months after (more...)

PL/SQL Fehlerbehandlung

Ja, es ist richtig: meine Einträge hier werden in letzter Zeit kürzer und kürzer. Daran werde ich aber auch heute nichts ändern, denn eigentlich will ich gerade nur einen Link unterbringen: Steven Feuerstein listet in seinem Artikel Nine Good-to-Knows about PL/SQL Error Management- nun ja: neun interessante Punkte auf, die man beim Exception Handling in PL/SQL berücksichtigen sollte. Zu den wichtigsten Hinweisen gehören aus meiner Sicht:
  • "An exception raised does not automatically roll back (more...)

Bind Variables

This example, tested on Oracle 11, shows how you can define bind variables in SQL*Plus, assign values to them in PL/SQL then display those values afterwards back in SQL*Plus:

SQL> variable bv1 varchar2(3)
SQL> variable bv2 number
SQL> begin
  2  select 'ABC' into :bv1 from dual;
  3  select 123 into :bv2 from dual;
  4  end;
  5  /

PL/SQL procedure successfully completed.

SQL> print bv1


SQL> print bv2


#DB12c feature – Secure External Procedures with DBMS_CREDENTIAL

Oracle Database 12c enables enhanced security for extproc by authenticating it against a user-supplied credential. This new feature allows the creation of a user credential and links it with a PL/SQL library object. Whenever an application calls an external procedure, the extproc process authenticates the connection before loading the shared library. The DBMS_CREDENTIAL package is … Continue reading

Temporal validity, multiple end dates

Recently I got involved in a question on Temporal Validity Periods together with Chris Saxon, one of the askTom-answer team.

The question was along the lines of: "What if I have a single start date but two possible end dates. One of the end dates is filled automatically by a background proces (could be a job) while the other one is to signal that the end date is set manually by the user. Could you (more...)

Designing PL/SQL Programs: Series home page

Designing PL/SQL Programs is a succession of articles published the articles in a nonlinear fashion. Eventually it will evolve into a coherent series. In the meantime this page serves as a map and navigation aid. I will add articles to it as and when I publish them.


Designing PL/SQL Programs

Principles and Patterns

Introducing the SOLID principles
Introducing the RCCASS principles
The Dependency Inversion Principle: a practical example

Software Architecture

Interface design

Tools and Techniques