Knowledge base: Excel, SQL, Python, Power BI, Tableau and statistics

How to use the knowledge base

I collected short entries on the functions and commands that keep coming back in everyday data analysis. Each one answers a single question: what the function does, what its syntax looks like and what to watch out for in an example. You do not need to read them in order. Type a function name into the search box or open a section and browse its groups.

When I return to a function I have not used for a while, I check the syntax and one simple example first. Then I look at the edge cases: empty cells, NULL, duplicates and the argument separator in localised Excel. That is why SQL entries point out when the syntax depends on the database engine.

Keeping entries current

Tools change. Excel gets new array functions, SQL engines extend their syntax and pandas removes old methods. I am reviewing the entries one by one and correcting names, examples and descriptions of current behaviour. An updated entry has a yellow bar on its left edge in the grid.

An entry answers a quick question about one function. When you want to see several functions working together on one task, read the articles on the blog. They walk through complete examples, from raw data to a checked result.