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Introduction
Conversion rates
Time to first order
Conversion charts
15. Multiple metrics in one query
Summary

## Instruction

Well done! The CASE WHEN construction can also be used to show multiple metrics in a single query. Take a look:

SELECT
COUNT(CASE
WHEN registration_date >= '2016-01-01'
AND registration_date <  '2017-01-01'
THEN customer_id
END) AS registrations_2016,
COUNT(CASE
WHEN registration_date >= '2017-01-01'
AND registration_date <  '2018-01-01'
THEN customer_id
END) AS registrations_2017
FROM customers;


We use COUNT() with a CASE WHEN inside. The purpose is to count only the users in each column who match the given criteria. For instance, the registrations_2016 column checks if the registration_date is in 2016. If it is, the customer_id is counted. If the condition isn't satisfied – and there is no alternative condition or ELSE part – CASE WHEN returns NULL and the customer isn't counted.

COUNT(CASE WHEN...) is a technique used to include multiple metrics in different columns of the same report.

## Exercise

Show two metrics in two different columns:

1. order_on_registration_date – the number of people who made their first order within one day from their registration date.
2. order_after_registration_date – the number of people who made their first order after their registration date.

### Stuck? Here's a hint!

Calculate the first metric in the following way:

COUNT(CASE WHEN first_order_date - registration_date = INTERVAL '0' day THEN customer_id END)