SUM, AVERAGE, COUNT, MIN and MAX

This demo will use the iris dataset.

When selecting data, aggregated output can be returned. The most common aggregation functions are: SUM, AVERAGE, COUNT, MIN and MAX.

Example 1: What is the sum of all the petal widths?

sqldf("
  SELECT SUM(`Petal.Width`) FROM iris;      
")

##   SUM(`Petal.Width`)
## 1              179.9

Example 2: What is the average sepal length?

sqldf("
  SELECT AVG(`Sepal.Length`) FROM iris;      
")

##   AVG(`Sepal.Length`)
## 1            5.843333

Example 3: How many rows are in the iris dataset?

sqldf("
  SELECT COUNT(Species) FROM iris  
")

##   COUNT(Species)
## 1            150

Example 4: What is the smallest petal length?

sqldf("
  SELECT MIN(`Petal.Length`) FROM iris;      
")

##   MIN(`Petal.Length`)
## 1                   1

Example 5: How long is the longest petal?

sqldf("
  SELECT MAX(`Petal.Length`) FROM iris;      
")

##   MAX(`Petal.Length`)
## 1                 6.9

All functions are relatively easy to implement, the difficulty is realising when you should be using each!