The following is my query:
select c.cust_lname, c.cust_fname, o.amount
from CUSTOMER c, orders o
where o.amount >
(select AVG (o.amount)
from orders o
group by order_num
having o.amount > AVG(o.amount));
Why is this not working?
The way you are writing the query, it would look like:
select c.cust_lname, c.cust_fname, o.amount
from CUSTOMER c join
orders o
on c.customerId = o.customerId
where o.amount > (select AVG (o.amount)
from orders o)
Note that you need to join together the two tables to get what you want.
You overengineered it. Take the having clause out of your subquery.
select c.cust_lname, c.cust_fname, o.amount
from CUSTOMER c, orders o
where o.amount >
(select AVG (amount) from orders );
Related
I have two tables, customers and orders, and I want to get the number of orders made by each customer.
I tried
SELECT orders.order_id, customers.customer_id,
FROM customers
INNER JOIN orders ON orders.customer_id = customers.customer_id
but I can't count number of orders
You are describing aggregation:
SELECT c.customer_id, count(*) no_orders
FROM customers c
INNER JOIN orders o ON o.customer_id = c.customer_id
GROUP BY c.customer_id
If you also want customers that have no order, use a LEFT JOIN instead, or a correlated subquery:
SELECT
c.customer_id,
(SELECT COUNT(*) FROM orders o WHERE o.customer_id = c.customer_id) no_orders
FROM customers c
Two tables named Sales.Customers and Sales.Orders.
Sales.Customers has a foreign key relationship to a column
named CustomerID in Sales.Orders.
Requirement: A query that returns all the customers. The query must also return the number of orders that each customer placed.
Query 1:
SELECT cust.cutomername,
NumberofOrders= COUNT(ord.OrderID)
FROM Sales.Customers Cust
LEFT JOIN
Sales.Orders Ord
ON Cust.CustomerID=Ord.OrderID
GROUP BY
Cust.CutomerName;
But I'm thinking of below one also,
Query2:
SELECT cust.cutomername,
NumberofOrders= COUNT(Cust.cutomerID)
FROM Sales.Customers Cust
LEFT JOIN
Sales.Orders Ord
ON Cust.CustomerID=Ord.OrderID
GROUP BY
Cust.CutomerName;
From both which one do you recommend & why?
This query:
SELECT c.customername, COUNT(o.OrderID)
FROM Sales.Customers c LEFT JOIN
Sales.Orders o
ON c.CustomerID = o.OrderID
GROUP BY c.CustomerName;
Probably returns all customers with meaningless counts -- probably 0 except for OrderIDs that happen to match CustomerIDs.
You probably intend:
SELECT c.customername, COUNT(o.OrderID)
FROM Sales.Customers c LEFT JOIN
Sales.Orders o
ON c.CustomerID = o.CustomerId
GROUP BY c.CustomerName;
In this query, the COUNT() is counting the number of matching orders. It can take the value of 0 for customers with no orders.
For this query:
SELECT c.customername, COUNT(c.OrderID)
FROM Sales.Customers c LEFT JOIN
Sales.Orders o
ON c.CustomerID = o.CustomerID
GROUP BY c.CustomerName;
The COUNT() is returning the number of rows. Every customer has at least one row, so the value would never be 0. Normally, you want the previous query.
Maybe this is your solution:
select c.Customername,
NumberOfOrders = (select count(o.OrderID) from Sales.Orders o where o.CustomerID = c.CustomerID)
from Sales.Customers c
order by c.Customername
Write a SELECT statement that returns three columns:
EmailAddress, OrderID, and the order total for each customer.
To do this, you can group the result set by the EmailAddress and OrderID columns.
In addition, you must calculate the order total from the columns in the OrderItems table.
SELECT c.EmailAddress, oi.OrderID, (oi.ItemPrice * oi.Quantity) -
oi.DiscountAmount
FROM Customers c JOIN Orders o ON c.CustomerID = o.CustomerID
JOIN OrderItems oi ON o.OrderID = oi.OrderID
GROUP BY c.EmailAddress, oi.OrderID
You are looking for GROUP BY and SUM():
SELECT c.EmailAddress, oi.OrderID,
SUM(oi.ItemPrice * oi.Quantity - oi.DiscountAmount)
FROM Customers c JOIN
Orders o
ON c.CustomerID = o.CustomerID JOIN
OrderItems oi
ON o.OrderID = oi.OrderID
GROUP BY c.EmailAddress, oi.OrderID;
Column must appear in the GROUP BY clause or be used in an aggregate function. Your column
(oi.ItemPrice * oi.Quantity) - oi.DiscountAmount
does not satisfy this requirement. I assume what you want to do is
sum((oi.ItemPrice * oi.Quantity) - oi.DiscountAmount)
?
I know similar questions like this have been asked before, but I have not seen one for more than 2 tables. And there seems to be a difference.
I have three tables from which I need fields, customers where I need customerID and orderID from, orders from which I get customerID and orderID and lineitems from which I get orderID and quantity (= quantity ordered).
I want to find out how many customers bought more than 2 of the same item, so basically quantity > 2 with:
SELECT COUNT(DISTINCT custID)
FROM customers
WHERE EXISTS(
SELECT *
FROM customers C, orders O, lineitems L
WHERE C.custID = O.custID AND O.orderID = L.orderID AND L.quantity > 2
);
I do not understand why it is returning me the count of all rows. I am correlating the subqueries before checking the >2 condition, am I not?
I am a beginner at SQL, so I'd be thankful if you could explain it to me fundamentally, if necessary. Thanks.
You don't have to repeat customers table in the EXISTS subquery. This is the idea of correlation: use the table of the outer query in order to correlate.
SELECT COUNT(DISTINCT custID)
FROM customers c
WHERE EXISTS(
SELECT *
FROM orders O
JOIN lineitems L ON O.orderID = L.orderID
WHERE C.custID = O.custID AND L.quantity > 2
);
I would approach this as two aggregations:
select count(distinct customerid)
from (select o.customerid, l.itemid, count(*) as cnt
from lineitems li join
orders o
on o.orderID = l.orderId
group by o.customerid, l.itemid
) ol
where cnt >= 2;
The inner query counts the number of items that each customer has purchased. The outer counts the number of customers.
EDIT:
I may have misunderstood the question for the above answer. If you just want where quantity >= 2, then that is much easier:
select count(distinct o.customerid)
from lineitems li join
orders o
on o.orderID = l.orderId
where l.quantity >= 2;
This is probably the simplest way to express the query.
I suggest you to use "joins" ,
Try this
select
count(*)
From
orders o
inner join
lineitems l
on
l.orderID = o.orderID
where
l.quantity > 2
I am counting how many times a company has ordered. Then I am only showing if a company has ordered less than 5 times. I am then checking it against the table with all company names to see what company has not ordered, which would not show up on the order table, then add their name on the displayed list.
What I have tried:
Select Orders.CustomerID, Count(Orders.CustomerID) AS OrderCount
From Orders Left Join Customers
On Orders.CustomerID = Customers.CustomerID
Group By Orders.CustomerID
Having Count(Orders.CustomerID) <5
This is totally wrong:
Select CustomerID
From Customers
Where EXISTS
(Select CustomerID, Count(CustomerID) AS 'OrderCount'
From Orders
Group BY CustomerID
Having Count(Orders.CustomerID) < 5)
I need to somehow compare the list of names before I ask it to see which ones have ordered less than 5 times.
Thanks
If you want to use LEFT JOIN, interchange the table names since you want to show values from Customers, otherwise use RIGHT JOIN instead.
SELECT Customers.CustomerID,
COUNT(Orders.CustomerID) AS OrderCount
FROM Customers
LEFT JOIN Orders
ON Orders.CustomerID = Customers.CustomerID
GROUP BY Customers.CustomerID
HAVING COUNT(Orders.CustomerID) < 5
using EXISTS()
SELECT CustomerID
FROM Customers c
WHERE EXISTS
(
SELECT 1
FROM Orders o
WHERE o.CustomerID = c.CustomerID
GROUP BY CustomerID
HAVING COUNT(CustomerID) < 5
)
Try this:
SELECT C.CustomerID, C.CustomerName, COUNT(O.CustomerID) AS OrderCount
FROM Customers C
LEFT JOIN Orders O ON O.CustomerID = C.CustomerID
GROUP BY C.CustomerID
HAVING OrderCount < 5
ORDER BY OrderCount, C.CustomerName