Everything Oracle SQL
This is the written version of a lesson from my SQL Course, in which I introduce students to the awesome and very commonly used SQL GROUP BY clause. If you want to follow along, here is the script you can use to create the employee table used in these examples: TablesCreation-script. In a previous lesson […]
This is the written version of a lesson from my SQL Course, in which I show how to use the FIRST and LAST functions. Like some other functions you probably know, these functions can be used either as aggregate functions or as analytic functions. I will show you how to use them as aggregate functions […]
I recently received a question about Pairwise Subqueries from one of the students in my SQL course, and I thought it would be a good idea to make my answer a blog post, since I did a couple of Google searches and didn’t find a lot of articles explaining the concept, so, this post is […]
I decided to write this article because the question about COUNT(*) Vs COUNT(1) keeps being asked, and I usually find myself explaining my answer again and again and/or looking for links to someone else’s articles that can help support my answer. Here I discuss a couple of common misconceptions and share a short but irrefutable […]
I’m writing this post as a contribution to the OTN appreciation day because I think Tim Hall’s idea was awesome. If I have to choose the feature I like and enjoy the most, it has to be the power of Oracle’s SQL implementation. I love how you can perform very complex tasks in a very […]
Ranking functions are some of the most commonly used analytic functions, and although the “ranking” category can quickly make you think about Top-N queries, that is actually not the only type of problems you can solve with them. In this short post, I demonstrate another common use of the ranking functions in SQL. For an […]
I decided to write about the Pivot and Unpivot clauses, because I find them very useful and powerful. In this article I will try to explain how they are used and show you some examples of the things you can do with them. These are features that were added in version 11g of the database, […]
Analytic functions in Oracle SQL are very useful and are utilized by many people, but sometimes without completely understanding how they work or what data they operate on. This article does not focus on a specific function, but on analytic functions in general. I decided to write it because I have seen people being confused […]
One of the most basic tasks you need to perform when tuning SQL statements is determining the causes of the performance problem, and to do that, you will most likely need to analyze the execution plan of the problematic statement. In this article, I cover the basics of execution plans, with the goal of helping […]
I decided to write about Top-N queries today because even though there are lots of articles and documentation about the correct way to do it in Oracle out there, I have seen this question asked on different forums, and to my surprise, many times people suggesting incorrect ways to do it without anyone clarifying their […]