比较以前的平均值和当前的平均值

Question

I have a table like the following:

Date | Person | Amount_Spent
42500  A        100 
42499  A        90 
42498  A        95

I would like a query that can take the current date (stored as excel dates) and show people where the difference between the amount spent on a given date (42500 in this case), ie 100 and the average of the last 3 days (ie 42500 >= x >= 42498) for example, ie 95 is greater than a certain amount, ie 2.

In this example the output should be:

Person
A   

Please ensure that the solution is able to cope with the fact that there will be multiple different people, some people won't spend every day also, so the query should only average the values in the average window, I guess it should include GROUP BY as a way of grouping people together.

Thanks!

Answer 1

Let's break this down into two pieces:

1. Calculate the AVG on a given date:

   SELECT AVG(Amount_Spent) FROM table_name WHERE DATE IN (42500, 42499, 42498);

2. Retrieve all Person matching the criteria:

   SELECT Person FROM table_name WHERE DATE IN (42500, 42499, 42498) AND Amount_Spent >= (SELECT AVG(Amount_Spent) FROM table_name WHERE DATE IN (42500, 42499, 42498));

This assumes the dates are stored as integers and that you'd like the average computed on a subset of dates. Only Persons who spent an amount greater than the average on those dates are retrieved.