Join With Where Clause - Nested Join/Where? - mysql

I've been trying to look for examples that better match my specific needs but I can't seem to find any.
I've got the following SQL statement, which works like a charm:
SELECT
customers.id,
customers.customer_name,
SUM(shipments.balance) AS shipmentBalance
FROM customers
LEFT JOIN shipments ON customers.id = shipments.bill_to
GROUP BY customers.id, customers.customer_name
ORDER BY shipmentBalance DESC;
But, I would like to be able to add a where condition to the JOIN, as I don't want ALL of the shipments balances being SUMMED up, rather only the ones that have balances greater than their related payment distribution amounts.
At this point, in a separate query, I can pull the shipments with balances that are greater than their payment distribution amounts using the following query:
SELECT
shipments.id,
shipments.pro_number,
shipments.balance,
SUM(payments_distributions.amount) AS Sum
FROM
shipments
LEFT JOIN payments_distributions ON shipments.pro_number = payments_distributions.shipment_id
WHERE balance > (SELECT IFNULL(SUM(payments_distributions.amount),0) FROM payments_distributions WHERE payments_distributions.shipment_id = pro_number)
GROUP BY shipments.id,shipments.pro_number;
But I'm not sure how to combine them.

Place the filter of the Shipment table in the ON clause:
SELECT
customers.id,
customers.customer_name,
SUM(shipments.balance) AS shipmentBalance
FROM customers
LEFT JOIN shipments ON customers.id = shipments.bill_to
AND balance > (SELECT IFNULL(SUM(payments_distributions.amount),0)
FROM payments_distributions
WHERE payments_distributions.shipment_id = pro_number)
GROUP BY customers.id, customers.customer_name
ORDER BY shipmentBalance DESC;

Related

More than 1 rows returned from SELECT inside SELECT

I'm trying to create a query to find what is the total amount owed by each customer to the company. It is the GROUP BY customerNumber in the sub query that is creating the problem.
SELECT customerName,
customers.customerNumber,
SUM(quantityOrdered * priceEach) - ( SELECT SUM(amount) AS MoneyPayed FROM payments GROUP BY customerNumber ) AS AmountOwed
FROM payments
INNER JOIN customers ON payments.customerNumber = customers.customerNumber
INNER JOIN orders ON customers.customerNumber = orders.customerNumber
INNER JOIN orderdetails ON orders.orderNumber = orderdetails.orderNumber
GROUP BY customerNumber;
The tables I'm trying to link are payments and orderdetails.
When I get rid of the GROUP BY I get results in negatives as the total SUM of amount is subtracted from each row of SUM(quantityOrdered * priceEach).
How can I change this so that I can return multiple rows from payments to subtract from SUM(quantityOrdered * priceEach) from the order details table.
Link to DB as StackOverflow doesn't allow me to post images
Thanks for help, sorry if format is bad, this is my first post.
You will need a couple of subqueries to meet your requirement. Let us break it down.
First, you need the total value of orders from each customer. You're very close to the correct query for that. It should be
SELECT orders.customerNumber,
SUM(orderdetails.quantityOrdered * orderdetails.priceEach) owed
FROM orders
JOIN orderdetails ON orders.orderNumber = orderdetails.orderNumber
GROUP BY orders.customerNumber
This subquery's result set gives customerNumber and owed, the amount owed. Notice that orders::orderdetails is a one::many relationship, so we're sure we're counting each detail just once, so the SUMs will be correct.
Next we need the amount paid by each customer. This subquery is fairly simple.
SELECT customerNumber,
SUM(amount) paid
FROM payments
GROUP BY customerNumber
Now for the operation you're missing in your question: we need to join these two subqueries to your customers table.
SELECT customers.customerName, customers.customerNumber
owed.owed - paid.paid balance
FROM customers
LEFT JOIN (
SELECT orders.customerNumber,
SUM(orderdetails.quantityOrdered * orderdetails.priceEach) owed
FROM orders
JOIN orderdetails ON orders.orderNumber = orderdetails.orderNumber
GROUP BY orders.customerNumber
) paid ON customers.customerNumber = paid.customerNumber
LEFT JOIN (
SELECT customerNumber,
SUM(amount) paid
FROM payments
GROUP BY customerNumber
) owed ON customers.customerNumber = owed.customerNumber
See how this works? We join a table and two subqueries. Each subquery has either zero or one rows for each row in the table, so we need not use SUMs or GROUP BY in the outer query.
There's only one complication left: what if a customer has never paid anything? Then the value of paid.paid will be NULL after the LEFT JOIN operation. That will force the value of owed - paid to be NULL. So we need more smarts in the SELECT statement to yield correct sums.
SELECT customers.customerName, customers.customerNumber
COALESCE(owed.owed,0) - COALESCE(paid.paid,0) balance
...
COALESCE(a,b) is equivalent to if a is not null then a else b.
Pro tip In queries or subqueries with JOIN operations, always mention table.column instead of just column. The next person to work on your query will thank you.

How to make my WHERE clause not run a syntax error in SQL?

The questions asks,
"Write a query to display the customer name and the number of payments they have made where the amount on the check is greater than their average payment amount. Order the results by the descending number of payments."
So far I have,
SELECT customerName,
(SELECT COUNT(checkNumber) FROM Payments WHERE
Customers.customerNumber = Payments.customerNumber) AS
NumberOfPayments
FROM Customers
WHERE amount > SELECT AVG(amount)
ORDER BY NumberOfPayments DESC;
But I am getting a syntax error every-time I run out. What am I doing incorrectly in this situation?
The syntax error comes from the fact that you are having an incorrect second subquery: amount > SELECT AVG(amount) doesn't work.
You could use amount > (SELECT AVG(amount) FROM Payments).
That is: complete the subquery and put it between ( ).
However this won't do what you want (plus it is inefficient).
Now since this is not a forum to do your homework for you, I will leave it at this and thus only help you with the actual question: why do you get the syntax error. Keep on looking, you will find it. No better way to learn than to search and find yourself.
I would phrase this as an inner join between the two tables, with a correlated subquery to find the average payment amount per customer:
SELECT
c.customerName,
COUNT(CASE WHEN p.amount > (SELECT AVG(p2.amount) FROM Payments p2
WHERE p2.customerName = c.customerName)
THEN 1 END) AS NumberOfPayments
FROM Customers c
INNER JOIN Payments p
ON c.customerNumber = p.customerNumber
GROUP BY
c.customerNumber
ORDER BY
NumberOfPayments DESC;
Your current query is on the right track, but you need to do something called conditional aggregation to obtain the count. In this case, we aggregate by customer then assert that a given payment amount is greater than his average before we include it in the count.
I would approach this just using JOINs:
SELECT c.customerName,
SUM( p.amount > p2.avg_amount ) as Num_Payments_Larger_Than_Average
FROM Customers c LEFT JOIN
Payments p
ON c.customerNumber = p.customerNumber LEFT JOIN
(SELECT p2.customerNumber, AVG(amount) as avg_amount
FROM payments p2
GROUP BY p2.customerNumber
) p2
ON p2.customerNumber = p.customerNumber
GROUP BY c.customerNumber, c.customerName
ORDER BY Num_Payments_Larger_Than_Average;
Some notes about this answer. First, it uses LEFT JOIN and conditional aggregation. This allows the query to return customers with zero payments larger than their average -- that is, customers with no payments or all of whose payments are the same.
Second, it includes customerNumber in the GROUP BY. I think this is important, because it may be possible for two customers to have the same name.

SQL retrieving filtered value in subquery

in this cust_id is a foreign key and ords returns the number of orders for every customers
SELECT cust_name, (
SELECT COUNT(*)
FROM Orders
WHERE Orders.cust_id = Customers.cust_id
) AS ords
FROM Customers
The output is correct but i want to filter it to retrieve only the customers with less than a given amount of orders, i don't know how to filter the subquery ords, i tried WHERE ords < 2 at the end of the code but it doesn't work and i've tried adding AND COUNT(*)<2 after the cust_id comparison but it doesn't work. I am using MySQL
Use the HAVING clause (and use a join instead of a subquery).....
SELECT Customers.cust_id, Customers.cust_name, COUNT(*) ords
FROM Orders, Customers
WHERE Orders.cust_id = Customers.cust_id
GROUP BY 1,2
HAVING COUNT(*)<2
If you want to include people with zero orders you change the join to an outer join.
There is no need for a correlated subquery here, because it calculates the value for each row which doesn't give a "good" performance. A better approach would be to use a regular query with joins, group by and having clause to apply your condition to groups.
Since your condition is to return only customers that have less than 2 orders, left join instead of inner join would be appropriate. It would return customers that have no orders as well (with 0 count).
select
cust_name, count(*)
from
customers c
left join orders o on c.cust_id = o.cust_id
group by cust_name
having count(*) < 2

SQL Join, right ? left ? inner?

working with mySql I would like to list all purchases that customers made on a specific cathegory of products.
So, I had 3 tables: customers (idCustomer, Name) , cathegories (idCategory, CategoryName) and orders (idOrder, idCustomer, idCathegory, Qty, Price)
But I want a listing with ALL of the customers.
Not only the one who bought that specific idCategory
I thought something like:
select sum(Orders.Qty), Customers.Name
from Orders
right join Customers on Orders.idCustomer = Customer.idCustomer
where Orders.idCategory = 'Notebooks'
group by Orders.idCategory
but this statement only lists the records for customers who exists in Orders table.
And I want all of them ( the one who didnt buy, with qty =0 )
thanks in advance
Most people find left join easier to follow than right join. The logic for left join is to keep all rows in the first table, plus additional information from the remaining tables. So, if you want all customers, then that should be the first table.
You will then have a condition on the second table. Conditions on all but the first table should be in the on clause rather than a where. The reason is simple: when there is no match, then the value will be NULL and the where condition will fail.
So, try something like this:
select sum(o.Qty) as sumqty, c.Name
from Customers c left join
Orders o
on o.idCustomer = c.idCustomer and
o.idCategory = 'Notebooks'
group by c.Name;
Finally, the group by should have a relationship to the select clause.
Try this query
select sum(Orders.Qty), Customers.Name
from Customers
right join Orders on Customer.idCustomer = Orders.idCustomer and Orders.idCategory = 'Notebooks'
group by Customers.Name

Summing order totals Mysql

I'm fairly new to Mysql and need help trying to combine two mysql queries that give a "total" for each "storeid" from the orders total. I'm currently using two queries to get the result:
SELECT storeid, storenum, name FROM store ORDER BY storeid DESC
SELECT SUM((1+0.07125)*qty*discprice) as total FROM items WHERE orderid IN (SELECT orderid FROM orders WHERE store = '".$row['storeid']."' AND date >= '2012-01-01' AND date < '2013-01-01')
I'm running a while loop and running the second query with the "storeid". However, I know I can do this is one query and group by "storeid" and create a total for all stores combined. But I can't figure it out.
Thanks!
SELECT s.storeid, s.storenum, s.name
SUM((1+0.07125)*i.qty*i.discprice) AS total
FROM items AS i
LEFT JOIN orders AS o
ON i.orderid=o.orderid
LEFT JOIN stores AS s
ON o.store=s.storeid
WHERE o.date >= '2012-01-01'
AND o.date < '2013-01-01'
GROUP BY s.storeid, s.storenum, s.name;
The trick is to join the three tables and then use an aggregate function on the items table.
SELECT stores.storeid, stores.storenum, stores.name, SUM((1+0.07125)*items.qty*items.discprice) as total
FROM stores
LEFT JOIN orders ON orders.storeid=stores.storeid AND orders.date>='2012-01-01' AND orders.date<'2013-01-01'
LEFT JOIN items ON items.orderid=orders.orderid
GROUP BY stores.storeid, stores.storenum, stores.name
What this does it this:
It will select every store from the stores table, and sum up the orders in that store. I chose a LEFT JOIN instead of straight JOINs, so that stores without any order in that time span will still show up with a total of NULL.
P.S. I don't have a copy of your database's schema, above SQL query might not actually work as expected - it is just supposed to point you in the right direction.