I'm trying to group SUM(OrderDetails.Quantity) but keep getting the error Not in aggregate function or group by clause: org.hsqldb.Expression#59bcb2b6 in statement but since I already have an GROUP BY part I don't know what I'm missing
SQL Statement:
SELECT OrderDetails.CustomerID, Customers.CompanyName, Customers.ContactName, SUM(OrderDetails.Quantity)
FROM OrderDetails INNER JOIN Customers ON OrderDetails.CustomerID = Customers.CustomerID
WHERE OrderDetails.CustomerID = Customers.CustomerID
GROUP BY OrderDetails.CustomerID
ORDER BY OrderDetails.CustomerID ASC
I'm trying to create a table that shows customers and the amount of products they ordered, while also showing their CompanyName and ContactName.
Write this:
GROUP BY OrderDetails.CustomerID, Customers.CompanyName, Customers.ContactName
Unlike in MySQL, PostgreSQL, and standard SQL, in most other SQL dialects, it is not sufficient to group only by the primary key if you also want to project functionally dependent columns in the SELECT clause, or elsewhere. You have to explicitly GROUP BY all of the columns that you want to project.
Don't take the customer id from the orders table. Take it from the customers table. If you do so, this might work in your database:
SELECT c.CustomerID, c.CompanyName, c.ContactName, SUM(od.Quantity)
FROM OrderDetails od INNER JOIN
Customers c
ON od.CustomerID = c.CustomerID
GROUP BY c.CustomerID
ORDER BY c.CustomerID ASC;
Note that the WHERE clause does not need to repeat the conditions in the ON clause.
Your version won't work in standard SQL because od.CustomerId is not unique in OrderDetails. Many databases don't support this, so in these you need the additional columns:
SELECT c.CustomerID, c.CompanyName, c.ContactName, SUM(od.Quantity)
FROM OrderDetails od INNER JOIN
Customers c
ON od.CustomerID = c.CustomerID
GROUP BY c.CustomerID, c.CompanyName, c.ContactName
ORDER BY c.CustomerID ASC;
Even so, it is much, much better to take all columns from the same table. That would allow the SQL optimizer to use indexes on Customers.
Related
I'm new to SQL Server and I'm trying to do some exercises. I want to find customers who bought least on W3schools database. My solution for this case is:
Join Customers with OrderDetails via CustomerID
Select CustomerNames that have least OrderID appeared after using JOIN.
Here is my query:
SELECT COUNT(OrderID), CustomerID
FROM Orders
GROUP BY CustomerID
ORDER BY COUNT(CustomerID) ASC
HAVING COUNT(OrderID) = '1'
When I ran this query, message says "Syntax error near "Having". What happened with my query?
Please help me to figure out.
My solution for this case is:
Join Customers with OrderDetails via CustomerID
Select CustomerNames that have least OrderID appeared after using JOIN.
As #thorsten-kettner lamented:
You say in your explanation that you join and then show the customer
name. Your query does neither of the two things...
Furthermore, your question has severe grammatical errors making it hard to decipher.
I want to find customers who bought least on W3schools database.
Nonetheless,
The Try-SQL Editor at w3schools.com
To get the list of customers who have at least 1 order:
SELECT C.CustomerName FROM [Customers] AS C
JOIN [Orders] AS O
ON C.CustomerID = O.CustomerID
GROUP BY C.CustomerID
ORDER BY C.CustomerName
To get the list of customers who have exactly 1 order:
SELECT C.CustomerName FROM [Customers] AS C
JOIN [Orders] AS O
ON C.CustomerID = O.CustomerID
GROUP BY C.CustomerID
HAVING COUNT(O.OrderID) = 1
ORDER BY C.CustomerName
To get the customer who made the least number of orders:
Including the ones who made no order. Use JOIN instead of LEFT JOIN if you only want to consider the ones who made at least one order.
You can remove LIMIT 1 to get the whole list sorted by the number of orders placed.
SELECT C.CustomerName, COUNT(O.OrderID) FROM [Customers] AS C
LEFT JOIN [Orders] AS O
ON C.CustomerID = O.CustomerID
GROUP BY C.CustomerID
ORDER BY COUNT(O.OrderID), C.CustomerName
LIMIT 1;
Addendum
As commented by #sticky-bit ,
The ORDER BY clause has to come after the HAVING clause.
You want a TOP 1 WITH TIES query, something like this:
SELECT TOP 1 WITH TIES CustomerID
FROM Orders
GROUP BY CustomerID
ORDER BY COUNT(OrderID);
In case you are using MySQL, try the following version:
SELECT CustomerID
FROM Orders
GROUP BY CustomerID
HAVING COUNT(OrderID) = (
SELECT COUNT(OrderID)
FROM ORDERS
GROUP BY CustomerID
ORDER BY COUNT(OrderID)
LIMIT 1
);
I'm having trouble with a really simple left join statement that's driving me nuts
I wanted to count the numbers of orders from each customer, that's fine, but I want to display the name, and I'm joining with the customers table and trying to select the name and it says that CustomerName is not part of an aggregate function, it's really weird.
SELECT Customers.CustomerName as 'Name',
COUNT(*) AS 'Order Count'
FROM Orders
LEFT JOIN Customers
ON Orders.CustomerID = Customers.CustomerID
GROUP BY Customers.CustomerID
Thanks for any tips.
You need to count the rows from the orders table, and the left join should be in the other direction:
SELECT c.customerid,
c.CustomerName as "Name",
COUNT(o.customerid) AS "Order Count"
FROM Customers c
LEFT JOIN Orders o ON o.CustomerID = cs.CustomerID
GROUP BY c.CustomerID, c.customername;
count() will ignore NULL values that come into the result due to the outer join so it will count the number of orders for each customers. Customers without orders will be show with a zero count.
Include CustomerName in Group BY instead of CustomerID
SELECT Customers.CustomerName as 'Name', COUNT(*) AS 'Order Count'
FROM Orders LEFT JOIN Customers ON Orders.CustomerID = Customers.CustomerID
GROUP BY Customers.CustomerName
If you are using SQL Server then try using OVER() without Group BY
SELECT Customers.CustomerName as 'Name', COUNT(*) OVER (PARTITION BY Customers.CustomerName ORDER BY Customers.CustomerName)AS 'Order Count'
FROM Orders LEFT JOIN Customers ON Orders.CustomerID = Customers.CustomerID
Modify as below. column used in group by clause should be in column queried in select clause
SELECT Customers.CustomerName as 'Name',
COUNT(*) AS 'Order Count'
FROM Orders
LEFT JOIN Customers
ON Orders.CustomerID = Customers.CustomerID
GROUP BY Customers.CustomerName
I have just reordered your query,please try this it will definitely work for you.
SELECT Customers.CustomerName as 'Name',
COUNT(*) AS 'Order Count'
FROM Customers
LEFT JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
GROUP BY Customers.CustomerID
A simple approach to get all the columns in the customers table is to use a correlated subquery:
select c.*, -- or whatever columns you want
(select count(*)
from orders o
where o.CustomerID = c.CustomerID
) as order_count
from customers c;
Because this avoids the outer GROUP BY, this also has the advantage of having better performance in most databases, particularly with an index on orders(CustomerId). Plus, it returns 0 if the customer has no orders. And, it allows you to choose any or all of the columns from Customers.
The correct way to get the counts you want is to count a column from Orders:
SELECT c.CustomerName, c.CustomerID,
COUNT(o.CustomerId) AS Order_Count
FROM Customers c LEFT JOIN
Orders o
ON o.CustomerID = c.CustomerID
GROUP BY c.CustomerID, c.CustomerName;
Notes:
The Customers table goes first in the LEFT JOIN because presumably you want all rows in Customers.
Table aliases make the query easier to write and to read.
Do not use single quotes for column aliases, even if your database supports it. The best method is to choose aliases that do not need to be supported.
Include the CustomerId in the logic, just in case two customers have the same name.
Count a column from Orders so you get a count of 0 for customers with no orders.
SELECT ORDERS.ORDERID,
ORDERS.CUSTOMERID,
ORDERS.EMPLOYEEID,
ORDERDETAILS.PRODUCTID,
ORDERDETAILS.UNITPRICE,
ORDERDETAILS.QUANTITY,
COUNT(ORDERS.ORDERID)
FROM ORDERS
LEFT JOIN ORDERDETAILS ON ORDERS.ORDERID=ORDERDETAILS.ORDERID
GROUP BY ORDERDETAILS.ORDERID
ERROR:Column 'ORDERS.OrderID' is invalid in the select list because it
is not contained in either an aggregate function or the GROUP BY
clause.
For using aggregate function selected column will also need to include in group by clause
SELECT
ORDERS.ORDERID,ORDERS.CUSTOMERID,ORDERS.EMPLOYEEID,ORDERDETAILS.PRODUCTID,ORD ERDETAILS.UNITPRICE,ORDERDETAILS.QUANTITY,
COUNT(ORDERS.ORDERID)
FROM ORDERS LEFT JOIN ORDERDETAILS ON
ORDERS.ORDERID=ORDERDETAILS.ORDERID
GROUP BY ORDERDETAILS.ORDERID,ORDERS.CUSTOMERID,ORDERS.EMPLOYEEID,ORDERDETAILS.PRODUCTID,ORD ERDETAILS.UNITPRICE,ORDERDETAILS.QUANTITY
Presumably, you intend this:
SELECT o.ORDERID, o.CUSTOMERID, o.EMPLOYEEID,
COUNT(od.ORDERID) as NUM_PRODUCTS
FROM ORDERS o LEFT JOIN
ORDERDETAILS od
ON o.ORDERID = od.ORDERID
GROUP BY o.ORDERID;
This produces one row per ORDERID with a count of the number of products (or more specifically orderdetails rows) in each order.
Notes:
All unaggregated columns in the SELECT should be GROUP BY keys.
You don't want to include unaggregated columns from ORDERDETAILS in the SELECT, because then an ORDER might have multiple rows in the result set.
You do want to use table aliases, so the query is easier to write and to read.
I have two tables:
customers(id,first_name,last_name,email)
orders (id,order_date,amount,customer_id)
customer_id in the orders table is the foreign key for id in the customers table
I'm trying to run the following code on PostgreSQL and getting an error:
SELECT first_name,last_name,order_date, sum(amount)
FROM customers
INNER JOIN orders ON customers.id = orders.customer_id
GROUP BY orders.customer_id;
Can someone tell me what's wrong with my code?
Just aggregate by all the columns in the select that are not aggregated. Also, qualify the column names:
SELECT c.first_name, c.last_name, o.order_date, sum(o.amount)
FROM customers c INNER JOIN
orders o
ON c.id = o.customer_id
GROUP BY c.first_name, c.last_name, o.order_date;
If you want the sum per customer name, then remove the order_date:
SELECT c.first_name, c.last_name, sum(o.amount)
FROM customers c INNER JOIN
orders o
ON c.id = o.customer_id
GROUP BY c.first_name, c.last_name;
The following query is ANSI compliant and should run on Postgres without error:
SELECT c.id, c.first_name, c.last_name, SUM(o.amount)
FROM customers c
INNER JOIN orders o
ON c.id = o.customer_id
GROUP BY c.id;
I think the immediate cause of the error is that you were also selecting the order_date column while aggregating over customers. This does not make sense, because Postgres has no way of knowing which order you are referring to.
Typically it is not possible to select columns in a GROUP BY query which either do not appear in the clause itself or are inside an aggregate function such as MAX or SUM. However, we can select the customer columns in this case because the id functionally determines the values for the first and last names.
Note that if id is not a primary key column, then you should use the approach suggested by #Gordon.
Demo
I'd like someone who can explain me the logic difference between these two queries. Maybe you can explain performance difference also. (DB is Microsoft Northwind).
-- Join
select distinct c.CustomerID, c.CompanyName, c.ContactName from orders as o inner join customers as c
on o.CustomerID = c.CustomerID
-- SubQuery
select customerid, companyname, contactname, country from customers
where customerid in (select distinct customerid from orders)
Thanks in advance.
The first generates an intermediate result set with all orders for all customers. It then reduces them using select distinct.
The second just selects the customers without having to reduce them later. It should be much more efficient. However, the select distinct is not needed in the subquery (it is done automatically with in).
I would write the logic as:
select c.customerid, c.companyname, c.contactname, c.country
from customers c
where exists (select 1
from orders o
where o.customerid = c.customerid
);
This can readily make use of an index on orders(customerid).