In the following query of current/perspective customers, I need to display, CustomerID, Customer's LastName, along with a column that displays whether customer has placed at least one order or not.
But, as expected, it displays multiple records of a customer if the customer placed multiple orders (one-to-many relationship). Question: How can we display only one record per customer here since we need only to report whether or not a customer has placed at least one order?
SELECT c.customerID, o.OrderID, CASE When ISNULL(o.OrderID, 0) = 0 Then 0 Else
1 End as YesNO
FROM Customers c
LEFT JOIN Orders o
ON c.customerID = o.customerID
using outer apply()
select
c.customerID
, o.OrderID
, case when o.OrderID is null then 0 else 1 end as YesNO
from Customers c
outer apply (
select top 1 o.OrderID
from Orders o
where c.customerID = o.customerID
) o
You could also use o.OrderId is null instead of ISNULL(o.OrderID, 0) = 0.
using group by and min()
select
c.customerID
, min(o.OrderID) as OrderId
, case when min(o.OrderID) is null then 0 else 1 end as YesNO
from Customers c
left join Orders o
on c.customerID = o.customerID
group by c.CustomerID
Use the group by.
SELECT c.customerID, o.OrderID, CASE When ISNULL(o.OrderID, 0) = 0 Then 0 Else 1 End as YesNOFROM Customers cLEFT JOIN Orders o ON c.customerID = o.customerID GROUP BY c.customerID
If the description in your question is to be believed, i.e. you want to know whether a customer has placed an order but do not need a representative OrderId for each customer:
select C.CustomerId,
case when exists ( select 42 from Orders as O where O.CustomerId = C.CustomerId )
then 1 else 0 end as YesNo
from Customers as C;
Note that exists is more efficient than count when you don't need an exact number.
Related
The customers table has total 1000 customers of which 1500 placed orders in FY 2016. But we want to display all the customers with their total number of orders in FY 2016 whether a customer placed an order in that FY or not. But the following query in SQL Server 2012 is displaying only 1490.
What we may be missing here?
SELECT c.CustomerID, count(*) AS TotalOrders
FROM Customers c
LEFT JOIN Orders o ON c.CustomerID = o.CustomerID
WHERE o.FiscalYear = '2016'
GROUP BY c.CustomerID
UPDATE:
The following query returns only 1 more record (1491) - still missing 9 more records.
SELECT c.CustomerID, count(*) AS TotalOrders
FROM Customers c
LEFT JOIN Orders o ON c.CustomerID = o.CustomerID
AND o.FiscalYear = '2016'
GROUP BY c.CustomerID
You where clause is turning the left outer join into an Inner join.
Change it to AND:
SELECT c.CustomerID, count(o.CustomerID) AS TotalOrders
FROM Customers c
LEFT JOIN Orders o
ON c.CustomerID = o.CustomerID
AND o.FiscalYear = '2016' -- Here
GROUP BY c.CustomerID
The correct SQL is:
SELECT c.CustomerID, count(o.CustomerID) AS TotalOrders,
sum(count(o.CustomerID)) over () as TotalTotalOrders
FROM Customers c LEFT JOIN
Orders o
ON c.CustomerID = o.CustomerID AND o.FiscalYear = '2016'
GROUP BY c.CustomerID;
TotalTotalOrders should be all the orders (or at least the ones with valid customer ids).
This will list all customers, whether or not they have any orders regardless of the year in which the order was placed. The sum will then count all orders that were placed in 2016, ignore the rest, and return an intenger (i.e. it will never be null).
SELECT
c.CustomerID
,sum(case when o.FiscalYear = '2016' then 1 else 0 end) AS TotalOrders
FROM Customers c
LEFT JOIN Orders o
ON c.CustomerID = o.CustomerID
GROUP BY c.CustomerID
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 was going through an example of LEFT JOIN on w3schools.com.
http://www.w3schools.com/sql/sql_join_left.asp
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;
The above query will return me all customers with No Orders as NULL Order ID+ All customers having Orders with their Order Ids
How should I modify this query so that it returns All Customers with No Orders + All Customers having Orders with Order date as '1996-09-18'
Thanks in advance.
If you want customers with no orders and those with a specific order date, then you want a WHERE clause:
SELECT c.CustomerName, o.OrderID
FROM Customers c LEFT JOIN
Orders o
ON c.CustomerID = o.CustomerID
WHERE (o.CustomerID is NULL) OR (o.OrderDate = DATE '1996-09-18)
ORDER BY c.CustomerName;
If you wanted all customers with their order on that date (if they have one), then you would move the condition to the ON clause:
SELECT c.CustomerName, o.OrderID
FROM Customers c LEFT JOIN
Orders o
ON c.CustomerID = o.CustomerID AND o.OrderDate = DATE '1996-09-18
ORDER BY c.CustomerName;
Note the difference: the first filters the customers. The second only affects what order gets shown (and NULL will often be shown).
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
I have a table which has rows for each product that a customer has purchased. I want to output a column from a SELECT query which shows the time it takes to deliver said item based on whether the customer has other items that need to be delivered. The first item takes 5 mins to deliver and all subsequent items take 2 mins to deliver e.g. 3 items would take 5+2+2=9 mins to deliver.
This is what I have at the moment(Using the Northwind sample database on w3schools to test the query):
SELECT orders.customerid,
orders.orderid,
orderdetails.productid,
CASE((SELECT Count(orders.customerid)
FROM orders
GROUP BY orders.customerid))
WHEN 1 THEN '00:05'
ELSE '00:02'
END AS DeliveryTime
FROM orders
LEFT JOIN orderdetails
ON orderdetails.orderid = orders.orderid
This outputs '00:05' for every item due to the COUNT in my subquery(I think?), any ideas on how to fix this?
Try this
SELECT orders.customerid,
orders.orderid,
orderdetails.productid,
numberorders,
2 * ( numberorders - 1 ) + 5 AS deleveryMinutes
FROM orders
INNER JOIN (SELECT orders.customerid AS countId,
Count(1) AS numberOrders
FROM orders
GROUP BY orders.customerid) t1
ON t1.countid = orders.customerid
LEFT JOIN orderdetails
ON orderdetails.orderid = orders.orderid
ORDER BY customerid
Gregory's answer works a treat and here's my attempts
-- Without each product line item listed
SELECT O.CustomerId,
O.OrderId,
COUNT(*) AS 'NumberOfProductsOrderd',
CASE COUNT(*)
WHEN 1 THEN 5
ELSE (COUNT(*) * 2) + 3
END AS 'MinutesToDeliverAllProducts'
FROM Orders AS O
INNER JOIN OrderDetails AS D ON D.OrderId = O.OrderId
GROUP BY O.CustomerId, O.OrderId
-- Without each product line item listed
SELECT O.CustomerId,
O.OrderId,
D.ProductId,
CASE
WHEN P.ProductsInOrder = 1 THEN 5
ELSE (P.ProductsInOrder * 2) + 3
END AS 'MinutesToDeliverAllProducts'
FROM Orders AS O
INNER JOIN OrderDetails AS D ON D.OrderId = O.OrderId
INNER JOIN (
SELECT OrderId, COUNT(*) AS ProductsInOrder
FROM OrderDetails
GROUP BY OrderId
) AS P ON P.OrderId = O.OrderId
GROUP BY O.CustomerId,
O.OrderId,
D.ProductId,
P.ProductsInOrder
Final code is below for anyone interested:
SELECT O.CustomerId,
O.OrderId,
Group_Concat(D.ProductID) AS ProductID,
CASE COUNT(*)
WHEN 1 THEN 5
ELSE (COUNT(*) * 2) + 3
END AS 'MinutesToDeliverAllProducts'
FROM Orders AS O
INNER JOIN OrderDetails AS D ON D.OrderId = O.OrderId
GROUP BY O.CustomerId