There was SQL before window functions and SQL after window functions: that’s how powerful this tool is. Being that of a deal breaker unfortunately means that it can be quite hard to grasp the feature. This article aims at making it crystal clear so that you can begin using it today and are able to reason about it and recognize cases where you want to be using window functions.
7 Articles tagged “Tricks”
In a recent article Craig Kerstiens from Heroku did demo the really useful crosstab extension. That function allows you to pivot a table so that you can see the data from different categories in separate columns in the same row rather than in separate rows. The article from Craig is Pivoting in Postgres.
Pivoting a matrix, also known as a matrix transposition
Let’s do the same setup as he did, with a table containing some randomly generated data about hypothetical visits to a web page, say, by date then by operating system.
Tonight I had the pleasure to present a talk at the Dublin PostgreSQL User Group using remote technologies. The talk is about how to make the most ouf of PostgreSQL when using SQL as a developer, and tries to convince you to dive into mastering SQL by showing how to solve an application example all in SQL, using window functions and common table expressions.
When you do partition your tables monthly, then comes the question of when to create next partitions. I tend to create them just the week before next month and I have some nice nagios scripts to alert me in case I’ve forgotten to do so. How to check that by hand in the end of a month?
The PostgreSQL IRC channel is a good place to be, for all the very good help you can get there, because people are always wanting to remain helpful, because of the off-topics discussions sometime, or to get to talk with community core members. And to start up your day too.
This morning’s question started simple : “how can I check if today is the “first sunday fo the month”. or “the second tuesday of the month” etc?
The idea of the day ain’t directly from me, I’m just helping with a very thin subpart of the problem. The problem, I can’t say much about, let’s just assume you want to reduce the storage of MD5 in your database, so you want to abuse bit strings. A solution to use them works fine, but the datatype is still missing some facilities, for example going from and to hexadecimal representation in text.
The problem was raised this week on IRC and this time again I felt it would be a good occasion for a blog entry: how to load an XML file content into a single field?
The usual tool used to import files is COPY, but it’ll want each line of the file to host a text representation of a database tuple, so it doesn’t apply to the case at hand. RhodiumToad was online and offered the following code to solve the problem: