SQL

May 1, 2013 I saw a decent SQL brain teaser this morning in the comp.databases.oracle.server Usenet group.  The OP in the message thread is attempting to summarize data in one of his tables, with the summarizations broken down by month and then the week within that month.  Increasing the challenge, the OP required that the dates defining […]

April 25, 2013 Roughly 12 years ago I was attempting to analyze customer order changes that were received through electronic document interchange (EDI), specifically X12 830 documents that show order forecasted demand for specific part numbers.  At the time, the EDI data was partially transformed and inserted into an Oracle 8.0.5 database, while that data […]

Article #3 in my ongoing series covering SQL statistic functions in Oracle Database is now up. The topic is the median:
 
MEDIAN: For When You Don't Really Mean It
 
Median is useful in typifying a data set when the data might be skewed, or in the presence of extreme outliers. For example, the U.S. Census Bureau reports median household income for states and counties so as paint a picture unskewed by the presence of, say, Bill Gates or Warren Buffet living just down the street. To learn more, hit the link.

I've just put up the second in an ongoing series (I hope!) of articles on Oracle SQL's build-in statistical functions. The topic is standard deviation. The previous one, my first, is on the mean. Here are links to the two:
 
2. STDDEV: Standing Sentinel on Your Data
 
1. AVG: What Does it Mean?

March 9, 2013 I had a couple of spare minutes today, so I tried a couple of experiments with Oracle Database 11.2.0.2 just to see if I could produce some unexpected results. First, I will create a simple database table with two indexes: CREATE TABLE T1 (   N1 NUMBER,   V1 VARCHAR2(20),   D1 […]

February 7, 2013 (Back to the Previous Post in the Series) As I have mentioned a couple of times previously, I am not much of a fan of ANSI style joins – I prefer using the classical Oracle join syntax when possible.  I try to keep up with an ERP mailing list, and try to assist with […]

<..Part one intro and examples
<….Part two Permissions

I’ve noticed that there has not been a lot of traffic on this series on Row Level Security (data masking) so far – maybe due to how I am presenting the material? So here is a summary to date in picture/diagram format:

<..Part 1, introduction..
..Part 3 summary in pictures..>

In this second post on the topic of “an introduction to Row Level Security” I want to cover a few things about what permissions you need to implement RLS and some of the consequences. In my introduction in part one I just said my main user has “DBA type Privileges”.

{NB This is all on Oracle V11.2 and I believe everything below is applicable to V10 as well. Also, I should point out that I am not an Oracle security expert – but despite repeatedly saying this, it seems like at least once a year I am asked to improve a system’s security on the grounds of “more than we have now is an improvement”}.

I’ve been working a little on Row Level Security (RLS) recently and wanted to mention a few things, so first some groundwork.

If you want to limit the rows certain users can see, you might think to use views or you might think to use RLS (part of VPD – Virtual Private Database). You can also (from V10 I think) limit which columns users can see. An example is probably the best way to show this. I’m doing this on Oracle 11.2.0.3.

I have two users, MDW and MDW_OFFSHORE. MDW has DBA-type privileges and MDW_OFFSHORE has connect, resource and one or two other simple privs. I will now demonstrate creating and populating a simple table under MDW, adding RLS to it and how it alters what MDW_OFFSHORE sees.

November 9, 2012 I have not had a lot of time to browse through forums lately, but I noticed an interesting thread in the comp.databases.oracle.server Usenet group.  The OP in the thread was curious why quotes (double quotes) were required around a particular column when referenced in a SQL statement, because specifying quotes around the column […]