How to calculate average discount per order in SQL

What you need

Average discount per order is the total value of discounts and coupons given in a period divided by the number of orders, including orders that had no discount. You need these columns, here from the sample file monthly.csv:

• discounts: discounts given
• orders: orders

CREATE TABLE monthly (
  month TEXT,          -- 'YYYY-MM'
  discounts INTEGER,
  orders INTEGER
);

Step by step

1. Load monthly.csv into a table called monthly. The table only needs the month column and the columns below.
2. Run the first query to get one row per month.
3. Run the whole-period query. It adds up each column first and divides once; averaging the monthly results gives a different, usually wrong, answer.

The queries

SELECT
  month,
  ROUND(1.0 * discounts / NULLIF(orders, 0), 2) AS discount_per_order
FROM monthly
ORDER BY month;

SELECT ROUND(1.0 * SUM(discounts) / NULLIF(SUM(orders), 0), 2) AS discount_per_order
FROM monthly;

What you should get

Run against the sample data, the code above returns these values:

₹2,20,400 ÷ 4,796 = ₹45.95

Notes for SQL

• Integer columns divide as integers in PostgreSQL, SQLite and SQL Server, so 3 / 4 gives 0. Multiplying by 1.0 (or 100.0) first makes the division decimal.
• NULLIF(x, 0) turns a zero denominator into NULL, so the query returns NULL for that row instead of failing with a division-by-zero error.
• Tested on SQLite and DuckDB. SUM, NULLIF and ROUND work the same in PostgreSQL, MySQL and BigQuery; SQL Server uses TOP instead of LIMIT where a query has one.

Where average discount per order misleads

• Decide whether free shipping counts as a discount. Either is fine; switching between them is not.
• Divide by all orders, not only discounted orders, unless you mean "average discount when a discount is used", which is a different metric.
• Store credit and loyalty points redeemed are discounts too, even when your platform reports them as a payment method.

The full explanation, with a calculator, is on the Average discount per order page.

Same metric, other tools

• Average discount per order in Excel and Google Sheets
• Average discount per order in Python (pandas)

Related metrics in SQL

• How to calculate discount rate in SQL
• How to calculate average order value in SQL
• How to calculate gross margin in SQL

Learn more about SQL

• Python and SQL for data analysis, side by side — 3 min read
• How to find out what changed in your sales data — 2 min read

About the data on this page

The figures come from a small made-up dataset, printed above in full so you can check every number by hand. Download it as monthly.csv. The results are computed from those rows when the page is built, and the Excel formulas, SQL and Python on these pages are run against the same rows before publishing, so the code and the answers agree.

To get these numbers from your own data without writing formulas, try AnalyzeIt: ask in plain words and it shows the working behind every figure.