welcome

Few (but meaningful) words about this blog


Welcome to Oracle Findings!
My name is Roberto Rigliaco and as you can easily imagine I’m passionate for database technologies. I’ve been working on Oracle RDBMS for many years and I decided to share my discoveries hoping you will find them as interesting as I do. I just want to clarify that these are my personal findings, things I have learned working on Oracle databases. You might read posts talking about similar topics on other blogs, I’m only reporting and sharing my direct experience.
All your comments are more than welcome.
Enjoy!

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How to easily test a complex REF CURSOR


In my personal experience, quite often I came across the need to test and optimize queries used by REF CURSORS. Sometimes it’s a really painless operation, other times it can really be a very long and complex operation that can make you waste a lot of time. Let’s see what we would normally do in a simple case: consider a procedure GET_DATA which returns a SYS_REFCURSOR

The query used for the ref cursor is quite simple, it extracts 3 columns and uses just one parameter as a filter. In such case, if I wanted to test the query, I would probably take it outside and run it manually to perform my test.

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Switching between range and interval partitioning: automatically create partitions in a range-partitioned table


INTERVAL partitioning has been introduced by Oracle as an extension of RANGE partitioning. There are few limitations like the fact that’s not supported at subpartition level and the partitioning key has to be a DATE or NUMBER but also some interesting advantages. When a table is partitioned by INTERVAL, in fact, partitions are created automatically as data is loaded into the table so we don’t have to bother creating anything in advance. We might, anyway, prefer to maintain our historical data in tables that are partitioned by RANGE. This because it’s common to keep inside the system a “rolling window” (e.g. last 90 days) of historical data meaning oldest partitions are dropped as soon as they become obsolete and with INTERVAL partitioning the last partition in the range section cannot be dropped. Moreover, in many processes it’s preferrable to have a full control of which partitions are created because data loaded into the system is not guaranteed to be “clean” and rows that don’t map to existing partitions have to be rejected.
After all these considerations, let’s have a look at what we can do to make the best out of both partitioning options (tested on 11g).

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Granting INDEX privilege gives access to your data


In this post I’ll show how incredibly easy is to read data from a table by having only the INDEX privilege granted on it. It’s something I found out when preparing a demo about Oracle Virtual Private Database, you’ll see why later on in this post.
Let’s imagine the following scenario: user SCOTT owns a table CUSTOMERS_CC holding sensitive information about customers

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How to use a custom index on primary key constraints


I admit it, I had a completely wrong belief when thinking about primary key constraints and their related index. When creating a PK on a table, Oracle automatically associates a unique index to it

The index name is internally generated and associated to the constraint. Fact is that, as I discovered some time ago, it’s not the index that enforces the uniqueness but the constraint itself. The constraint uses the underlying index to go faster but the index itself does not enforce anything. But you can’t really blame me for thinking differently in the beginning, not after seeing that Oracle creates a unique index for the pk!

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How to use RETURNING INTO with a multi-row insert


The RETURNING INTO clause is a very convenient way to retrieve values from rows that are being inserted/deleted/updated. When used with UPDATE and DELETE statements, it’s possible to retrieve values of multiple rows by using the RETURNING BULK COLLECT INTO. This is something that does not work with the INSERT statements: in that case you will be able to only return values from a single row.
Let’s see how this works and create a simple test table that will be the target of our DML operations

First of all let’s use a simple case just to have a look at how this works.

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Oracle Virtual Private Database is not so private!


Virtual Private Database (Oracle VPD) was introduced by Oracle in release 8i. It’s a security feature that provides access restriction at row/column level for privacy and regulatory compliance. It allows sophisticated logic to be applied through the use of custom functions in which rules can be written for fine-grained data access. If you want to know more about how it works check the official documentation.
The point of this post is that the column-level security of Oracle VPD can be easily tricked! It all started when I decided to check the new Redaction feature released with Oracle 12c. This is somehow similar to VPD but it works at a different level. I came across a very interesting article from David Litchfield that in his article demonstrates how this feature is broken and not safe at all. Well, starting from there I made my own similar investigations on VPD and got some really surprising results.

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How locks work with move partition ONLINE on Oracle 12c


With the release 12c Oracle introduced the “online partition movement” making the operation a non-blocking DDL command. This means that it’s possible to run any DML on a partition while the same is being “moved” using the new ONLINE option.
Let’s see how that works on our usual test table populated with 1 million rows in the first partition

We can now take a look at how move partition works normally when not running it in ONLINE mode.
Let’s execute

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SQL Plus and the dark power of the character # (hash or pound)


Not everybody knows that in SQL Plus the character # (called hash or pound) has a special use that I discovered it myself not much time ago. Well, it’s not really a secret, you can read about it on the official SQL Plus manual, but it’s rarely used. The sign #, in fact, is the default character used as SQLPREFIX during a SQL Plus session and can be changed executing the command

SET SQLPRE[FIX] prefix_char

But what does it do? It tells SQL Plus to execute a SQL Plus command while in the middle of entering a SQL statement or a Pl/Sql block of code.
For example you are writing a select statement

and, while writing down the list of columns to extract, you don’t remember the name of one of them. Normally you would quit writing the query, execute a desc of the table and start writing it again from scratch. But the # sign give us another possibility. All you have to do is enter a new line, digit the magic sign # and write the desc you need

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Partial indexing for unique indexes on Oracle 12c


With release 12c Oracle has introduced partial indexing, the possibility to define partial local indexes on partitioned table. This is an interesting feature that allows to save some space getting rid of index segments for old partitions. Let’s quickly see how this works.
First of all, when creating a partitioned table, the INDEXING property can be specified to define if we want or not to create the indexes for that partition (default value is ON unless a different default is set at table level)

This property can also be changed in a second time issuing a simple alter command

The local indexes need to be created with the option INDEXING PARTIAL otherwise they will not be affected by the INDEXING ON/OFF property set at partition/subpartition level.
There is a restriction though: local unique indexes cannot be created as partial so it’s not possible to drop partitions of a unique index. Well, this is at least what Oracle says but let’s go on.

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