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Window Functions

Introduction
Quick refresher
PARTITION BY ORDER BY with ranking
PARTITION BY ORDER BY with window frames
PARTITION BY ORDER BY with analytical functions
16. LEAD() with PARTITION BY ORDER BY
Summary

Instruction

Now, let's talk about the use of analytical functions with PARTITION BY ORDER BY. Take a look at the following example:

SELECT
  country,
  city,
  opening_day,
  LEAD(city, 1, 'NaN') OVER(PARTITION BY country ORDER BY opening_day)
FROM store;

In the above example, we show the country, city and opening_day of each store, but we also show the city where the next store was opened – in the same country, of course.

Exercise

For each store, show the sales in the period between August 5, 2016 and August 10, 2016: store_id, day, number of transactions, number of transactions on the previous day and the difference between these two values.

Stuck? Here's a hint!

Use LAG(transactions).