Skip to 0 minutes and 2 seconds Let’s explore how you can use SQL to perform some analytics on a computer sales database. If you want to see the total number of sales, we use the count function, like in this SQL statement. So it can account all the records from the sales table. Let’s execute this. So it returns the total of 7,069. So that’s the 7,069 sales have taken place. But what if you want to put a date range in? Let’s put the WHERE clause in. So we’ve got WHERE sales date is after the 1 of January, 2019, and before the 31 of January 2019. Let’s execute this. So the sales have gone down because it’s only one month, to 514.
Skip to 0 minutes and 59 seconds You could also find the total value of sales using the SUM function. So here we’ve used the SUM function, and we’re asking it for the sum of price from the sales table. Let’s run this.
Skip to 1 minute and 16 seconds So the total number of price is 251,835. Or the average income per sale. Let’s have a look at that. So we use the AVG function of price from the sales table.
Skip to 1 minute and 38 seconds Let’s execute this. So the average income for each sale is in the middle of around 35 pounds. You can also specify how data should be grouped together, such as sales grouped by employee. So in this statement, we’re counting. So we’re using the count function from the sales table, but we’re going to group it by the employee ID.
Skip to 2 minutes and 8 seconds OK, so that’s given us the total sales for each employee, but we don’t know what the employee ID is. We haven’t asked for a return of the employee ID. In this statement, we’ve asked for the employee ID to be returned, and also order in descending order, the total sales. So if we run this one, we can see that hpatel has a total sales of 2,405, the most. And at the bottom with 1,282 is mhogan. How could you use the aggregate function, SUM and GROUP BY, to create a league table of the computers which generate the most income from sales? Share your thoughts in the comments below.
In the previous step, you learnt about data analytics; now you are going to use SQL to perform some, specifically analysing data of computer sales.
Download and open this version of the computer sales database, which contains the 2019 sales records for a fictitious company that sells Raspberry Pi computers.
To recap, the
sales table holds data about each sale made by the company. There is a record for each sale, containing the
model_id of the computer sold, the date it was sold, the
employee_id of the person who made the sale, and the price it sold for.
Browse the data in the
sales table and you will see that there are sales record for every day between
Count, sum, and average
COUNT function can be used in a
SELECT statement to return the number of records contained in a query.
Run the following query to return the total number of sales:
SELECT COUNT(*) FROM sales
This SQL query returns the total number of computer sales in 2019.
Currently, the field returned is named
COUNT(*). You can change the field name using the
SELECT COUNT(*) AS total_sales FROM SALES
As with any other
SELECT query, a
WHERE clause can used to filter the results. By filtering the results between two dates, you can modify the query to show total sales for January 2019.
SELECT COUNT(*) as january_sales FROM sales WHERE sale_date >= '2019-01-01' AND sale_date <= '2019-01-31'
Two other useful SQL functions for analysing data in databases are
SUM could be used to find the total value of sales by adding up the
price of all sales:
SELECT SUM(price) as total_value FROM sales
AVG can be used to return the average income per sale:
SELECT AVG(price) as average_income FROM sales
AVG are examples of aggregate functions. Aggregate functions bring data together and provide a summary. In the examples above, the data within the
sales data is aggregated to provide a single count, sum, or average.
You can specify how data should be aggregated, or grouped together, by using a
GROUP BY statement.
The SQL statement below returns total sales, but includes a
GROUP BY employee_id statement.
SELECT COUNT(*) AS total_sales FROM sales GROUP BY employee_id
What do you think the four rows that are returned represent?
The four records returned are the total sales made by each employee.
GROUP BY employee_id statement specified that the
COUNT of sales should be aggregated, or split, by the
employee_id. As there are four different instances of
employee_id in the
sales table, four counts were returned.
To create a league table of sales by employee, modify the query to add the
employee_id to the
SELECT statement and order the results by the
SELECT COUNT(*) AS total_sales, employee_id FROM sales GROUP BY employee_id ORDER BY total_sales DESC
How could you use the aggregate functions
GROUP BY to create a league table of the computers that generated the most income from sales? Discuss your thoughts in the comments section.