SQL: Need to SUM on results that meet a HAVING statement - sql

Question

I have a table where we record per user values like money_spent, money_spent_on_candy and the date.
So the columns in this table (let's call it MoneyTable) would be:
UserId
Money_Spent
Money_Spent_On_Candy
Date
My goal is to SUM the total amount of money_spent -- but only for those users where they have spent more than 10% of their total money spent for the date range on candy.
What would that query be?
I know how to select the Users that have this -- and then I can output the data and sum that by hand but I would like to do this in one single query.
Here would be the query to pull the sum of Spend per user for only the users that have spent > 10% of their money on candy.
SELECT
UserId,
SUM(Money_Spent),
SUM(Money_Spent_On_Candy) / SUM(Money_Spent) AS PercentCandySpend
FROM MoneyTable
WHERE DATE >= '2010-01-01'
HAVING PercentCandySpend > 0.1;

Answer 1

You couldn't do this with a single query. You'd need a query that could reach back in time and retroactively filter the source table to handle only users with 10% candy spending. Luckily, that's kind of what sub-queries do:
SELECT SUM(spent) FROM (
SELECT SUM(Money_Spent) AS spent
FROM MoneyTable
WHERE (DATE >= '2010-01-01')
GROUP BY UserID
HAVING (SUM(Money_Spent_On_Candy)/SUM(Money_Spent)) > 0.1
);
The inner query does the heavy lifting of figuring out what the "10%" users spent, and then the outer query uses the sub-query as a virtual table to sum up the per-user Money_Spent sums.
Of course, this only works if you need ONLY the global total Money_Spent. If you end up needing the per-user sums as well, then you'd be better off just running the inner query and doing the global total in your application.

Answer 2

You can use common table expressions. Like this:
WITH temp AS (SELECT
UserId,
SUM(Money_Spent) AS MoneySpent,
SUM(Money_Spent_On_Candy)/SUM(Money_Spent) AS PercentCandySpend
FROM MoneyTable
WHERE DATE >= '2010-01-01'
HAVING PercentCandySpend > 0.1)
SELECT
UserId
SUM(MoneySpent)
FROM UserId

Answer 3

Or you can use a derived table:
SELECT SUM(Total_Money_Spent)
FROM ( SELECT UserId, Total_Money_Spent = SUM(Money_Spent), SUM(Money_Spent_On_Candy)/SUM(Money_Spent) AS PercentCandySpend
FROM MoneyTable
WHERE DATE >= '2010-01-01'
HAVING PercentCandySpend > 0.1 ) x;