Here you'll find explanations for the following functions and examples of how to use each one.

- Row count
- Sum
- Count unique values
- Average
- Max
- Min

*To provide context for examples, we'll use the following data table showing reservations for an imaginary car rental company.*

## Count rows

The count function **counts the total number of rows** containing each of the distinct values in a specific column.

**Examples**

To see the number of reservations associated with each of the car brands, you would calculate the count broken down by the makecolumn:

To see the number of reservations associated with each of the car brands on each of the pick up days, you would calculate the countbroken down by the pick up and also the make column:

## Sum

The sum function sums the values in a specific column.

**Examples**

To see the total amount paid for reservations for each of the car brands, you would calculate the sum of the price column broken down by the make column:

You could also see the total amount paid for all of the reservations by calculating the sum of the price column, and not specifying a column to break the results down by:

## Count unique values

The count unique values function **counts the number of unique values** in a specific column.

It's particularly useful for situations where a particular value exists in multiple rows but you only want to count it once.

**Example**

Let's say we wanted to find the amount of revenue each sales person had generated by selling extras (sat nav, child seats etc). To do this, we'd have to join the sales person table, the reservations table, and the extras table together. It would look like this:

To find the total revenue per sales person, we could just calculate the sum of the price column, and break the results down by the name column.

But, what if we wanted to add some extra context by including a count of the reservations? The problem is, we can't simply count the rows by the reservations ID column because, since we've joined the extras table in and each reservation can be associated with multiple extras, it's possible that there are now multiple rows for each reservation. In fact, if you check the first reservation in the table above (ID 81), you'll see it appears in two rows (since it has two extras associated with it).

The solution is to use the **count unique values** function. So, starting from the table above, we can 1. calculate the sum of the pricecolumn and 2. count the unique values in the reservations ID column, and break both down by the name column. The result would look like this:

## Average

The average function calculates the average of the values in a specific column.

**Examples**

To see the average price paid per reservation, you would calculate the average of the price column, not broken down by anything:

To see the average price paid for reservations of each the different car brands, you would calculate the average of the price column broken down by the make column. The result would be:

## Max

The max function returns the highest value in a specific column. If the column contains date values, the highest value is the most recent date.

**Example**

To see the most recent reservation for each of the car models, you would calculate the max of the pick up column broken down by the modelcolumn:

## Min

The min function returns the smallest value in a specific column. If the column contains date values, the smallest value is the least recent date.

**Examples**

To see the lowest price paid for a reservation, you would calculate the min of the pick up column:

To see the lowest price paid on each of the pick up days, you would calculate the min of the price column, broken down by the pick upcolumn: