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Evaluation Order and Common Problems
Window functions and GROUP BY
Summary and Review

## Instruction

Great! We can also use LEAD and LAG with grouped rows. The query below creates day-to-day deltas. Take a look:

SELECT
EndDate,
SUM(FinalPrice) AS SumPrice,
LAG(SUM(FinalPrice)) OVER(ORDER BY EndDate ASC)
FROM Auction
GROUP BY EndDate
ORDER BY EndDate ASC;


This shows each end date with

1. the total price of all items sold on that day and
2. the total price of all items sold on the previous day.

## Exercise

For each end date, show the following:

• the EndDate
• the sum of views from auctions that ended on that day (name this column SumViews)
• the sum of views from the previous day (name this column PreviousDay)
• the difference between the sum of views on that day and on the previous day (name this column Delta)

### Stuck? Here's a hint!

You will have to use:

LAG(SUM(Views))

in the window function.