How to calculate support contact rate in SQL

What you need

Support contact rate is the number of support tickets per 100 orders: tickets divided by orders, times 100. You need these columns, here from the sample file monthly.csv:

• orders: orders
• support_tickets: support tickets

CREATE TABLE monthly (
  month TEXT,          -- 'YYYY-MM'
  orders INTEGER,
  support_tickets 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(100.0 * support_tickets / NULLIF(orders, 0), 2) AS contact_rate
FROM monthly
ORDER BY month;

SELECT ROUND(100.0 * SUM(support_tickets) / NULLIF(SUM(orders), 0), 2) AS contact_rate
FROM monthly;

What you should get

Run against the sample data, the code above returns these values (in percent):

2,148 ÷ 4,796 × 100 = 44.79%

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 support contact rate misleads

• One customer writing three times about the same order is one problem. Count conversations, not messages.
• Contacts before purchase (pre-sales questions) are good contacts; separate them.
• Orders and tickets are in different months for slow problems; look at a rolling period.

The full explanation, with a calculator, is on the Support contact rate page.

Same metric, other tools

• Support contact rate in Excel and Google Sheets
• Support contact rate in Python (pandas)

Related metrics in SQL

• How to calculate first contact resolution rate in SQL
• How to calculate return rate in SQL
• How to calculate RTO rate 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.