Introduction

In the previous chapter, we discussed how to use SQL to prepare datasets for analysis. Once the data is prepared, the next step is to analyze the data. Generally, data scientists and analytics professionals will try to understand the data by summarizing it and trying to find high-level patterns in the data. SQL can help with this task primarily through the use of aggregate functions: functions that take rows as input and return one number for each row. In this chapter, we will discuss how to use basic aggregate functions and how to derive statistics and other useful information from data using aggregate functions with GROUP BY. We will then use the HAVING clause to filter aggregates and see how to clean data and examine data quality using aggregate functions. Finally, we look at how to use aggregates to understand data quality