In this problem, you need to calculate the mean number of items per order based on a table that provides the count of items per order and the number of such orders. Let’s walk through how to write an SQL query to find the mean number of items per order, rounded to one decimal place.

Problem Overview

You have a table named items_per_order that includes two columns:

• item_count: Represents the number of items in an order.
• order_occurrences: Indicates how many orders had that specific item_count.

Your task is to compute the mean number of items per order. The result should be rounded to one decimal place.

Table: items_per_order

Example Data:

Desired Output:

Explanation:

• To find the mean number of items per order, you calculate the total number of items and divide it by the total number of orders. Here’s the breakdown of the calculations:
• Total Items: ( (1 \times 500) + (2 \times 1000) + (3 \times 800) + (4 \times 1000) = 8900 )
• Total Orders: ( 500 + 1000 + 800 + 1000 = 3300 )
• Mean: ( \frac{8900}{3300} = 2.7 )

SQL Query Breakdown

To calculate this, you need to:

1. Compute the total number of items.
2. Calculate the total number of orders.
3. Determine the mean number of items per order.
4. Round the result to one decimal place.

Here’s how you can write the SQL query:

SELECT 
    ROUND(
        SUM(item_count * order_occurrences) / SUM(order_occurrences),
        1
    ) AS mean
FROM 
    items_per_order;

Query Explanation:

1. Calculating Total Items:

• SUM(item_count * order_occurrences): This multiplies the item_count by the order_occurrences for each row and then sums up these values to get the total number of items.

1. Calculating Total Orders:

• SUM(order_occurrences): This sums up all order_occurrences to get the total number of orders.

1. Computing the Mean:

• SUM(item_count * order_occurrences) / SUM(order_occurrences): This calculates the mean by dividing the total number of items by the total number of orders.

1. Rounding the Result:

• ROUND(..., 1): Rounds the mean value to one decimal place for a cleaner and more readable result.

1. Aliasing the Result:

• AS mean: Labels the result column as mean for clarity.

Conclusion

This SQL query helps you determine the average number of items per order by calculating a weighted mean based on the given data. By summing up the total items and dividing by the total number of orders, then rounding the result, you get a precise and understandable measure of order size.