Aggregate Functions

The essence of reporting is typically to distill a population of data into a value or values representing a trend or summary. This is what aggregation is all about. Aggregate functions answer the questions asked by the consumers of data:

• “What were the total sales of chicken gizzard by-products for last month?“
• “What is the average price paid for food condiments by male Brazilians between the ages of 19 and 24?”
• “What was the longest order-to-shipping time of all orders last quarter?”
• “Who is the oldest employee still working in the mail room?”

Aggregate functions return a scalar value (a single value) applying a specific aggregate operation. The return data type is comparable to that of the column or value passed to the function. Aggregates are often used along with grouping, rollup, and pivoting operations to produce results for data analysis. This is covered in greater detail in Chapter 7. The focus here is on some of the more common functions in simple SELECT queries.