Eager Aggregation in SQL queries

Aggregation is a widely used way to summarize the content of a database. It is usually expressed with GROUP BY clause or just using aggregate functions (like COUNT or SUM). When the database engine executes a query with aggregations, it produces individual rows need to compute the required output and then performs the aggregation as (almost) last step. We discuss in this article how to re-write a query manually so that the order of operations will be different and when it can be beneficial.

Creating Aggregates

An Overview of PostgreSQL Window Functions

This article looks at Window functions and how they can be used to solve problems in a different way from standard aggregate functions.

Getting Subtotals

Handling Aggregations on a Poorly Designed Database

When the database design is not great, you may have to write some creative queries to get what you need.

Optimize Your SQL by Reformulating the Spec

As SQL developers, we tend to think of performance tuning in terms of crafting the best table indices, avoiding scalar and table valued functions, and analyzing query plans (among other things). But sometimes going back to the spec and applying some properties of elementary math can be the best way to begin to improve performance of SQL queries which implement mathematical formulas. This article is a case study of how I used this technique to optimize my SQL implementation of the Inverse Simpson Index.

Cube v rollup

Round averages

Not Again!

NULL Aggregates