In my career, I’ve heard many times, things like “How to write a complex SELECT query?”, “Where to start from?” or “This query looks so complex. How you’ve learned to write such complex queries?”. While I would like to think of myself as of a brilliant mind or genius or add something like “query magician” to my social network profiles, well, writing complex SQL wouldn’t be the only thing required to do that. Therefore, in this article, I’ll try to cover the “magic” behind writing complex SELECT statements.

Today, data is the basis of any business. The world of enterprise computing is the epitome of data-driven businesses. The importance of structured storage of data is unquestionably in the focus. And at this time, with the computing model quickly shifting towards the cloud, and storage costs falling rapidly, enterprises are leveraging data more and more to tune their businesses.

SQL has many cool features and aggregate functions are definitely one of these features, actually functions. While they are not specific to SQL, they are used often. They are part of the SELECT statement, and this allows us to have all benefits of SELECT (joining tables, filtering only rows and columns we need), combined with the power of these functions.

SQL join multiple tables is one of the most popular types of statements executed while handling relational databases. As known, there are five types of join operations: Inner, Left, Right, Full and Cross joins.

If you want to get something meaningful out of data, you’ll almost always need to join multiple tables. In this article, we’ll show how to do that using different types of joins. To achieve that, we’ll combine INNER JOINs and LEFT JOINs. So, let’s start.