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Introduction
Customer registration
Customer cohorts
Summary
14. Summary

## Instruction

Perfect! It's time to wrap things up. What have we learned in this section?

1. To count registrations during a given period of time, use:
SELECT COUNT(CustomerID) AS ...
FROM customers
WHERE RegistrationDate >= ...
AND RegistrationDate <  ...;

2. To count registrations from the current period (e.g., the current year), use:
SELECT COUNT(CustomerID) AS RegistrationCount
FROM Customers
WHERE RegistrationDate >= DATEADD(year, DATEDIFF(year, 0, GETDATE()), 0);

3. To show a report of registration counts for all years, use:
SELECT
DATEPART(year, RegistrationDate) AS RegistrationYear,
COUNT(CustomerID) AS RegistrationCount
FROM Customers
GROUP BY DATEPART(year, RegistrationDate)
ORDER BY DATEPART(year, RegistrationDate);

4. A customer cohort is a group of customers that share a common characteristic over a certain time period. To show annual registration cohorts per channel, use:
SELECT
DATEPART(year, RegistrationDate) AS RegistrationYear,
ChannelName,
COUNT(*) As RegistrationCount
FROM Customers Cu
JOIN Channels Ch
ON Cu.ChannelId = Ch.Id
GROUP BY DATEPART(year, RegistrationDate), ChannelId, ChannelName
ORDER BY DATEPART(year, RegistrationDate);


All right! How about a short quiz?

## Exercise

Click to continue.