Courses in Databases

I was preparing a post about what can slow down a query, but when I was reading a lot of different stuff online to make sure I am writing truth I encountered several interesting papers, and presentations that I think are worth reading. First of them is a series of presentations regarding Data Processing on ...

Know your database – a complex query

I have seen in my life many people learning SQL without prior understanding how databases work. But there are many crucial things that can make writing queries more fun, if it is not fun enough. Optimization in terms of memory use and execution is one of them. I would even say that is the most ...

FiFO with SQL

I am going to create small system/website that will allow me to manage my stocks, and monitor the portfolio. I do not have much of it, but I cannot access the data from wherever I want and it is not so dynamic. Beside the design itself I came across a problem of recreating a FIFO ...

BigData (R)evolution

I want to learn some more about the scale, but not scale in general but scaling data storing and processing. Nowadays if you hear about the big data, it often implies hadoop based distributed system. As Yahoo is one of the biggest contributors to Hadoop at the moment, the best tutorial is also on their ...

PostgreSQL 9.3

I did not realize that on my brithday PostgreSQL hit 9.3 mark (see a news). With this release there is a new join type that I first hear about. It is named LATERAL JOIN. There is no need for me to copy the documentation, so if you want to know what that is head to ...

No Duplicates in Subset

Yesterday I was helping a friend of mine with an interesting problem. There is a big table ~4MLN rows, it is wide (has many columns, lets say 30). We are interested in getting rows, which contain duplicates in 5 columns, we do not care what data are in other columns, at least not with regard ...

Few Words About Indexes

Writing the previous post it came to my mind, that many people may not be aware that using custom functions in WHERE clauses may be the reason why the index is not used. There are several facts about indexes you should keep in mind: index is most often a b-tree, see one of the Princeton’s lectures ...