# Lookup Model for Order Size

The previous model was a lookup model for classification, both for multiple classification and binary classification. The lookup itself was along a single dimension. This section uses lookup models for estimating a real number. It starts with the very simplest case, no dimensions, and builds the model up from there.

## Most Basic Example: No Dimensions

Another basic example of a lookup model is assigning an overall average value. For instance, we might ask the question: *Based on purchases in 2015, what do we expect the average order size to be in 2016?* The following query answers this question, by using the average of all purchases in 2015:

SELECT YEAR(o.OrderDate) as year, AVG(o.TotalPrice) as avgsize FROM Orders o WHERE YEAR(o.OrderDate) in (2015, 2016) GROUP BY YEAR(o.OrderDate) ORDER BY year

This query gives the estimate of $86.07. This is a reasonable estimate, but it is a bit off the mark because the actual average in 2016 is $113.19. The average could...