Constraint Optimization Summary

This is the last part of a series about Constraint Optimization.
In this post I’ll summarize the conclusions from the previous parts.

When we add a constraint to an existing table, there are two aspects that are worth taking into consideration:


When the table contains a significant number of rows, adding a constraint may take a lot of time. In some cases Oracle applies a very nice optimization that can reduce this time to (more...)

Introducing Elastic Search NoSQL to Oracle SQL developers – comparing dozens of ElasticSearch and SQL operations (a bit like Rosetta)

Even for organizations with strong roots in relational databases such as Oracle RDBMS, there may be valuable opportunities for leveraging additional data sources, for example to support special (search) use cases. Elastic Search (Index) is one of those data stores that can add value – for example to provide powerfur search capabilities to web applicaties, to handle metrics and logging output from live applications or to collect and analyze any data set in your landacape. (more...)

Adding a Unique Constraint in an Online Way

Note: unlike most of my posts, this one assumes using Enterprise Edition

I have a table t and I want to add a unique constraint on one of its columns – c1.

The Offline Way

The straightforward and most simple way to do it is using a single alter table statement:

SQL> alter table t add constraint c1_uk unique (c1);

Table altered.

By default, Oracle creates in this operation a unique constraint (named c1_uk) and (more...)

SQL Magic Squares – or Why the Optimizer does not like Magic

A long-time player at the Oracle Dev Gym tried his hand at generating Magic Squares using SQL.

When he attempted to tune his statement a bit, he was surprised that it didn't go a little faster as expected, rather it went from 2 minutes to 45 minutes? At that point he contacted me to see if I could explain the mystery...

So thank you, Hamid Talebian, for the interesting case. It was fun to play (more...)

Ergänzungen zu coalesce und NVL

Vor längerer Zeit hatte ich hier gelegentlich auf Artikel verwiesen, die sich mit dem unterschiedlichen Verhalten von NVL und coalesce beschäftigten und einerseits auf die short-circuit evaluation mit coalesce und andererseits auf deren Ausklammerung im Fall von Sequencen hinwiesen. Jetzt haben die Herren Lewis und McDonald dazu ergänzende Beobachtungen geliefert.
  • Jonathan Lewis weist darauf hin, dass coalesce beim costing schlechter abschneidet als NVL, weil es mit dem Standardwert von 1% für Gleichheit operiert, der für (more...)

Fast but Offline, or Online but Slow?

The Constraint Optimization series:

In the previous parts of this series I showed that Oracle does a nice optimization – that may save (more...)

How to fix queries on DBA_FREE_SPACE that are slow

I found myself in a situation where OpsView a monitoring tool, was having difficulty monitoring the tablespaces for a particular pluggable database.

Upon investigation it was found the queries against the dictionary table DBA_FREE_SPACE were taking a very long time:

SQL> set timing on
SQL> select nvl(sum(dfs.bytes)/1024/1024,0) from dba_free_space dfs where dfs.tablespace_name = 'USERS';


Elapsed: 00:00:10.98

There are 60 tablespaces in this pluggable database, which the time varied (more...)

Dynamic LOV with Pipeline function

A new year brought me some new tasks. I had to take over a generic Excel import and the customer wanted some extension by checking if the join on the master tables were successful.

Unfortunate we were talking about a generic solution which meant that all the configuration was saved inside tables including the LOV-tables which were saved as simple select statements.

Show all import rows/values which were not fitting towards the master data.


EBR – Part 5: Explicit Actualization of Dependent Objects

This is part 5 of a post series about EBR.
In part 1 we created the baseline model and code – a table (PEOPLE) and two packages (PEOPLE_DL and APP_MGR).
In part 2 we saw that even a simple change – a package body compilation – can be dangerous in a busy system.
In part 3 we learned about editions and how they can be used for solving the problems described in part 2, so (more...)

Data driven APEX icons

We have an application written with a heavily customised Theme 25 built for 10" tablets, and we feel the Universal Theme justifies the move, in part because of the surrounding ecosystem. Check out this forum discussion on the topic.

We've been looking through the packaged applications for applied ideas, and using the Universal Theme sample application as a component reference.

I came across a requirement where we had a list of items that indicated completion (more...)

JSON_TABLE and the Top 2000

Oracle database 12c provides native JSON parsing. It is relatively easy to go from data in a JSON format to a relational representation.
In this example I will use data from the Top 2000. Every year in The Netherlands a playlist is produced by popular vote and fully broadcast between Christmas and the last day of the year, with the number one being played just before the New Year. You can see the complete list (more...)

EBR – Part 4: Invalidation and Actualization of Dependent Objects

This is part 4 of a post series about EBR.
In part 1 we created the baseline model and code – a table (PEOPLE) and two packages (PEOPLE_DL and APP_MGR).
In part 2 we saw that even a simple change – a package body compilation – can be dangerous in a busy system.
In part 3 we learned about editions and how they can be used for solving the problems described in part 2, so (more...)

EBR – Part 3: Changing a Package Body (the Solution)

This is a link to an index page for all the parts of the series

This is part 3 of a post series about EBR.
In part 1 we created the baseline model and code – a table (PEOPLE) and two packages (PEOPLE_DL and APP_MGR).
In part 2 we saw that even a simple change – such as a package body compilation – can be dangerous in a busy system.
In this post we’ll see (more...)

Order of Predicate Execution #2

In the previous post I talked about the order of predicate execution based on the predicate position and inline view. As promised, in this post I’ll add statistics and see what happens. Creating extended statistics In this demo I’m using functions, so Oracle doesn’t really know what the output of the function is. That’s why … Continue reading Order of Predicate Execution #2

“Collection iterator pickler fetch”: pipelined vs simple table functions

Alex R recently discovered interesting thing: in SQL pipelined functions work much faster than simple non-pipelined table functions, so if you already have simple non-pipelined table function and want to get its results in sql (select * from table(fff)), it’s much better to create another pipelined function which will get and return its results through PIPE ROW().

A bit more details:

Assume we need to return collection “RESULT” from PL/SQL function into SQL query “select (more...)

DBMS_COMPRESSION can be run in parallel, at least from

I was trying to use DBMS_COMPRESSION on an 11gR2 ( on RHEL 6.3) database the other day and was helped by this article from Neil Johnson. I was having some trouble with permissions until I read that article which nicely summarises everything you need to know – thanks Neil!

One thing I did notice is that Neil stated that you can’t parallelise the calls to the advisor since it uses the (more...)

Type Dependent Tree

While trying to explain a student question about Oracle object types, it seemed necessary to show how to write a dependency tree. I did some poking around and found there wasn’t a convenient script at hand. So, I decided to write one.

This assumes the following Oracle object types, which don’t have any formal methods (methods are always provided by PL/SQL or Java language implementations):

( base_id  NUMBER  (more...)

Substitutable Columns

Oracle’s substitutable columns are interesting and substantially different than Oracle’s nested tables. The benefit of substitutable columns is that you can create one for an object type or any subtypes of that object type. Unfortunately, you can’t create the same behavior with nested tables because Oracle’s implementation of collection types are always final data types and you can’t extend their behaviors.

The Oracle Database has three types of collections. Two are SQL scoped collection types (more...)

Friday Fun SQL Lesson – union all

Our office kitchen is unavailable this Friday, so the call was put out for pub lunch.

After a couple of replies I decided to enter my reply, in full nerd mode.
select * from people_coming_to_lunch;


3 rows selected.
And of course one of the other SQL geeks (name redacted) replied to extend the data set.
select * from people_coming_to_lunch
select 'Shanequa'
from dual;
And I couldn't help myself. I (more...)

EBR – Part 1: Overview and Setup

I have been using EBR in a real production system for more than 4 years now.
EBR – an acronym for Edition-Based Redefinition – is a powerful and unique feature (or, more precisely, a set of features) that enables patching and upgrading live Oracle-based applications in an online fashion, with zero downtime.

As an Oracle Developer and DBA I find EBR one of the most important tools in my toolkit, and I take advantage of (more...)