Duncan Mein's Blog

In a recent application, we needed to model the Organisational Hierarchy which at its most complex ran to 7 levels deep. This was achieved using a self referencing foreign key (Pigs Ear) similar to that of the EMP table in the Scott schema. In essence, it simply stores the parent / child relationship for each entry in the Hierarchy. This approach serviced the application very well in that a simply tree walk (CONNECT BY PRIOR) allowed us to construct the Hierarchical tree and bounce our requests off that. During the production of the Discoverer End User Layer, it became evident that this Hierarchy needed to be flattened out (un-normalized) in order for it to reported on. This is because Discoverer (or any other BI product) does not support the CONNECT BY and START WITH clause. Discoverer needs to know how many levels exist within a Hierarchy and that every thread in the Hierarchy has the same number of levels in order to build a folder structure that can be reported on. After a bit of i...

It has always been a fairly rudimentary task pivoting a result set so that rows are displayed as columns. More recently I had the requirement to translate a result set the other way so that the columns would be displayed as rows. For Example Your result set starts out like this: SITE COST1 COST2 COST3 COST4 ------------------------------------------------------------------ SITE_ONE 2000 255 SITE_TWO 100 SITE_THREE 145 5000 The desired output should look like this: SITE VALUE ------------------------------ SITE_ONE 2000 SITE_ONE 255 SITE_TWO 100 SITE_THREE 145 SITE_THREE 5000 Thanks to the help from Mr. Tom Kyte at http://asktom.oracle.com I was a...

When your PL/SQL block errors, it has always been a rudimentary task in identifying the error generated using a combination of SQLCODE and SQLERRM. These 2 functions however do not tell us the exact line of code that propagated the error. This feature would be very handy when debugging code. In Oracle 10g, there is a function called: DBMS_UTILITY.format_error_backtrace This will return the line number that generated the error. It does not tell us what the SQL Error message is so I use it in conjunction with SQLERRM to quickly debug problematic code. In a recent application, I used it as part of my error logging and reporting function that allows the support team to quickly troubleshoot errors. The more information about the error we can give them, the quicker they should be able to response. At least that’s the theory. For a more detailed explanation of how to best utilise this function, have a look at this atricle

Well, our week skiing in Meribel came and went too quickly. We all had am awesome time in the "Best British Ski Resort" France has to offer. The Skiing was good (not excellent) but enough to thoroughly exhaust every one of us and our Chalet was very comfortable. Living costs in the Trois Valleys was not cheap however. Beer ranged between 8 and 10 Euros a pint which made for some very expensive nights out. Fortunately, food was included in our Chalet costs. I was devastated parting with 40 Euros for a lasagne, chips and a coke in Courcheval but hey. For anyone interested, some pictures can be found here I shall be putting them all on my website in the next few weeks.

For anyone who has manually written an Update Statement in a Web Application, the issue of Optimistic Locking always took a while to address. The normal convention is to use a series of hidden elements for every form element that is submitted and doing an "old vs new" comparison in the Update statement to see if any valus in the database have changed. I found the main drawback was the need to create large amounts of hidden elements that are then passed into the DML procedure for evaluation. I came across ORA_ROWSCN in 10GR2 that reduces the amount of hidden form elements you need to submit. Its basically a new pseudo column in that database that provides the SCN (System Clock Number for the last time the row was updated) associated with individual rows when they were read. The basic steps to utilise this approach are as follows: 1) create table users (id number, name VARCHAR2 (100), address VARCHAR2 (100), tel NUMBER) ROWDEPENDENCIES / ROWDEPENDENCIES need to set as SCN by de...

A while ago I came across an issue exporting the contents of a BLOB to a flat file on my file system. My processing was to upload a .csv file into the wwv_flows_files table, and write a file back to my Oracle directory using the UTL_FILE api. Upon inspecting the file produced, a newline character was inserted after every line. To cut a long story short, a colleague of mine came up with a workaround that involved parsing the newley produced file, removing any spurious lines and creating a new file minus the blank lines. As you can imagine, for large files, this added a fair amount of time to the Upload process. There is light at the end of the tunnel however. This article was sent to me by another colleague. At the end there is a solution to the problem. Cheers Kris " Oracle 10g includes extra open modes (rb, wr, ab) to signify byte mode operation. The "wb" open mode can be used along with the PUT_RAW procedure to prevent extra newline characters being added on a Wind...

The strangest thing happened the other day whilst performing an application import within Oracle XE. The import was successful but running the application however was less so. Some of my pages contained a lot of JavaScript in the HTML Header section of the Page Attributes. On some of these pages, the import appeared to add a carriage return to one of the lines and thus breaking my script. The knock on effect was that my application ground to a rather unimpressive halt. Without having the time to investigate why, I decided that it would be better to store all my JavaScript in a . js file on the server and write a reference to it on the pages where the scripts were needed. Once you have created your . js file (I store in a sub directory if the /i/ path) on the server, you can reference these files by adding the following to the HTML Header of your page: Storing your long JavaScript externally to your application also makes debugging a bit easier as well.