I’ve come across a very neat trick in Oracle that I thought I’d share. Its useful for situations where you can have circular references in the data diagram, for example when the table includes a column which is a reference for another entry in the same table. Usually it would be necessary to write some function which could be called recursively and allow you to traverse this tree layout, however in Oracle there is the CONNECT BY PRIOR syntax.

The users and groups example

Sticking with my earlier example let’s say I’ve got an employees table and the employee can have a manager, which is an employee

users

select first_name || ' ' || last_name, level
from users
connect by prior id = manager
start with id = 1

Will output the list of people followed by their reports. We can distinguish who is where in the tree using the magical column “level” which is available when we connect in this way. I’ve used the level to indent the name column by two spaces for each level down the tree the person is and to show their job title:

select lpad('  ', (level - 1) * 14) || first_name || ' ' || last_name, job_title
from users
connect by prior id = manager
start with id = 1

Today I’m working on a complicated database driven web page. I edit the source using vim on the main file server. In order to get the file onto the webserver, I then quit out of the file and a script checks my syntax and ftps the file into the correct location on the webserver. Once its there, my prompt returns and I know its time to refresh the web page. Which is interesting, but if you are still reading then you must be wondering what my point is.

Its this, the file check and write takes too long. Its not ages, its like, seven seconds. But its long enough for me to jump to the other window (or in this case, tab) and read the next headline in my feedreader, or the message in my chat window … and you can guess what happens next! I read the article, or reply to the message, or whatever. About three minutes later (if I’m lucky), I’ll remember to refresh the page, check my changes and go on with the task in hand.

This is why all programmers need fast hardware and efficient tools to develop with. My waiting attention span just isn’t long enough to wait more than about three seconds for compile/upload/reload/whatever else is needed. I think I can multitask but actually I end up distracting myself completely!

Speaking of which, my upload is finished ….

I need to operate on a big table with lots of records, but only on rows where the primary key starts with a number. Because obviously its a good idea to differentiate types of records in this way …. only joking! Its just one of those little tasks that crops up from time to time.

The Fast and Dirty Way

select code
from products
where substr(code,1,1) in (0,1,2,3,4,5,6,7,8,9)

Oracle Regular Expression Method

select code
from products
where regexp_like(code,'^[[:digit:]]')

Further Resources

I got this from this article on technology and also the definition of some of the character classes from this very helpful resource on psoug

I came across this when reading an article on Mike’s site yesterday:

_“The best advice I ever received from a manager is that it is easier to get forgiveness than permission.”

The article is at Top 3 Ways to Fight Bureaucratic Inertia in IT and it makes for interesting reading. More than once I’ve had projects cancelled or stalled indefinitely because of two superiors’ inability to agree on the requirements and Mike’s article has given me some ideas on how to manage this type of situation in the workplace.

Its a funny thing but the smallest details when you are looking for a job are actually the most important. I’ve never actually asked to see inside the ladies when I’ve been at a job interview but I’ve always wished I had once I got the job!

I’ve been a big fan of Joel Spolsky for some time, but he posted an advert to his site today that had me riveted. He’s looking for a sysadmin for Fog Creek, and in the advert he writes

“We’re still a small friendly company and we all eat lunch together every day at one big table.”

This is what I’m looking for in a company, this sums up my requirements for my entire working life, and he’s nailed it in a single sentence.