Alias name issue in SQL - sql-server

Question

I was trying to write a query for the SQL Server sample DB Northwind. The question was: "Show the most recent five orders that were purchased by a customer who has spent more than $25,000 with Northwind."
In my query the Alias name - "Amount" is not being recognized. My query is as follows:
select top(5) a.customerid, sum(b.unitprice*b.quantity) as "Amount", max(c.orderdate) as Orderdate
from customers a join orders c
on a.customerid = c.customerid
join [order details] b
on c.orderid = b.orderid
group by a.customerid
--having Amount > 25000 --throws error
having sum(b.unitprice*b.quantity) > 25000 --works, but I don't think that this is a good solution
order by Orderdate desc
Pls let me know what I am doing wrong here, as I am a newbie in writing T Sql. Also can this query and my logic be treated as production level query?
TIA,

Answer 1

You must use the aggregate in the query you have. This all has to do with the order in which a SELECT statement is executed. The syntax of the SELECT statement is as follows:
SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY
The order in which a SELECT statement is executed is as follows. Since the SELECT clause isn't executed until after the HAVING clause, you can't use the alias like you can in the ORDER BY clause.
FROM
WHERE
GROUP BY
HAVING
SELECT
ORDER BY
Reference Article: http://www.bennadel.com/blog/70-sql-query-order-of-operations.htm

Answer 2

This is a known limitation in SQL Server, at least, but no idea if it's a bug, intentional or even part of the standard. But the thing is, neither the WHERE or HAVING clauses accept an alias as part of their conditions, you must use only columns from the original source tables, which means that for filtering by calculated expressions, you must copy-paste the very same thing in both the SELECT and WHERE parts.
A workaround for avoiding this duplication can be to use a subquery or cte and apply the filter on the outer query, when the alias is just an "input" table:
WITH TopOrders AS (
select a.customerid, sum(b.unitprice*b.quantity) as "Amount", max(c.orderdate) as Orderdate
from customers a join orders c
on a.customerid = c.customerid
join [order details] b
on c.orderid = b.orderid
group by a.customerid
--no filter here
order by Orderdate desc
)
SELECT TOP(5) * FROM TopOrders WHERE Amount > 25000 ;
Interesting enough, the ORDER BY clause does accepts aliases directly.

Answer 3

You must use Where b.unitprice*b.quantity > 25000 instead of having Amount > 25000.
Having used for aggregate conditions. Your business determine your query condition. If you need to calculate sum of prices that have above value than 25000, must be use Where b.unitprice*b.quantity > 25000 and if you need to show customer that have total price above than 25000 must be use having Amount > 25000 in your query.
select top(5) a.customerid, sum(b.unitprice*b.quantity) as Amount, max(c.orderdate) as Orderdate
from customers a
JOIN orders c ON a.customerid = c.customerid
join [order details] b ON c.orderid = b.orderid
group by a.customerid
having sum(b.unitprice*b.quantity) > 25000 --works, but I don't think that this is a good solution
Order by Amount

Answer 4

I don't have that schema at hand, so table' and column' names might go a little astray, but the principle is the same:
select top (5) ord2.*
from (
select top (1) ord.CustomerId
from dbo.Orders ord
inner join dbo.[Order Details] od on od.OrderId = ord.OrderId
group by ord.CustomerId
having sum(od.unitPrice * od.Quantity) > $25000
) sq
inner join dbo.Orders ord2 on ord2.CustomerId = sq.CustomerId
order by ord2.OrderDate desc;

Answer 5

The Having Clause will works with aggregate function like SUM,MAX,AVG..
You may try like this
SELECT TOP 5 customerid,SUM(Amount)Amount , MAX(Orderdate) Orderdate
FROM
(
SELECT A.customerid, (B.unitprice * B.quantity) As "Amount", C.orderdate As Orderdate
FROM customers A JOIN orders C ON A.customerid = C.customerid
JOIN [order details] B ON C.orderid = B.orderid
) Tmp
GROUP BY customerid
HAVING SUM(Amount) > 25000
ORDER BY Orderdate DESC

Answer 6

The question is little ambiguos.
Show the most recent five orders that were purchased by a customer who
has spent more than $25,000 with Northwind.
Is it asking to show the 5 recent orders by all the customers who have spent more than $25,000 in all of their transactions (which can be more than 5).
The following query shows all the customers who spent $25000 in all of their transactions (not just the recent 5).
In one of the Subquery BigSpenders it gets all the Customers who spent more than $25000.
Another Subquery calculates the total amount for each order.
Then it gets rank of all the orders by OrderDate and OrderID.
Then it filters it by Top 5 orders for each customer.
--
SELECT *
FROM (SELECT C.customerid,
C.orderdate,
C.orderid,
B3.amount,
Row_number()
OVER(
partition BY C.customerid
ORDER BY C.orderdate DESC, C.orderid DESC) Rank
FROM orders C
JOIN
--Get Amount Spend Per Order
(SELECT b2.orderid,
Sum(b2.unitprice * b2.quantity) AS Amount
FROM [order details] b2
GROUP BY b2.orderid) B3
ON C.orderid = B3.orderid
JOIN
--Get Customers who spent more than 25000
(SELECT c.customerid
FROM orders c
JOIN [order details] b
ON c.orderid = b.orderid
GROUP BY c.customerid
HAVING Sum(b.unitprice * b.quantity) > 25000) BigSpenders
ON C.customerid = BigSpenders.customerid) X
WHERE X.rank <= 5