Null values in PostgreSQL
Before we dive into analysis, it is important to understand what null signifies and what we can do with it. Briefly, in Postgres, NULL has no value. It doesn’t equal 0, so you can’t use it in mathematical calculations. In a nutshell, it indicates a field without a value. In large datasets, it makes sense that not all columns contain data. In the case of OSM, perhaps that street has not been labeled with a name or the identity of that building is unknown. It doesn’t mean the value is nothing but that it is unknown. In the PostgreSQL database, there are different scenarios where NULL is the expected value – this differs in each coding language, so be vigilant (and curious).
The data we will use for the rest of this chapter can be found in the GitHub repository mentioned earlier and includes Rondinia.gdb. As a reminder, we will locate the downloaded files in the Browser area, add them to the canvas, and bring them into PostgreSQL...
