Just learning how to use common table expressions, I wish I was writing like this from the gate.
I've converted all of my queries in my database to a CTE format using WITH ... AS but this one and I am struggling .
So there are two tables:
Table 1. customers
customer_id: unique id for each customer
full_name: customer full name
Table 2. subscriptions
subscription_id: unique id for subscription
customer_id: id for customer who subscribed to subscription
title: name of subscription
The following query is used to return how many subscriptions each of your customers has:
SELECT c.customer_id, c.full_name,
(
SELECT COUNT(*)
FROM subscriptions s
WHERE s.customer_id = c.customer_id
GROUP BY s.customer_id
) subscriptions_count
FROM customers c
How can I rewrite this as a Common Table Expression?
If you really want to use CTE here is one way. You can rewrite it to use left join if you wish to show customers with no counts
with cte as
(select customer_id, count(*) as counts
from subscriptions
group by customer_id)
select c.customer_id, c.full_name, s.counts
from customers c
join cte s on s.customer_id=c.customer_id;
Sure. You can calculate the aggregate first, then join with customers:
WITH cte AS (
SELECT customer_id
, COUNT(*) AS n
FROM subscriptions
GROUP BY customer_id
)
SELECT c.*
, COALESCE(cte.n, 0) AS n
FROM customers AS c
LEFT JOIN cte
ON c.customer_id = cte.customer_id
;
Related
I am trying to select which co-ordinates from OA table are NOT found in the CUSTOMER address table.
SELECT DISTINCT
OA.CO_ORDS
FROM
CUSTOMER
INNER JOIN
OA ON customer.address=oa.co_ords
ORDER BY ID ASC;
Returns the co-ordinates which ARE in the customer table. How do I return those that are not in the customer table?
Am I also able to COUNT how many of customers are is in each co-ordinate (The co-ords are not specific and not accurate, this is purely for query testing only)
SELECT DISTINCT
OA.CO_ORDS
FROM
CUSTOMER
INNER JOIN
OA ON customer.address=oa.co_ords
ORDER BY ID ASC;
We can use NOT EXISTS to find those co-ordinates which don't appear in the customer table:
SELECT co_ords
FROM oa
WHERE
NOT EXISTS
(SELECT 1 FROM customers
WHERE address = oa.co_ords)
ORDER BY id;
In order to count how many customers belong to a certain co-ordinate, we can use COUNT with GROUP BY, something like this:
SELECT c.address, COUNT(*)
FROM customers c
JOIN oa
ON c.address = oa.co_ords
GROUP BY c.address;
It could be better to count a specific column instead of *.
It could also be better to use an IN clause instead of JOIN the tables:
SELECT c.address, COUNT(*)
FROM customers c
WHERE address IN
(SELECT co_ords FROM oa)
GROUP BY c.address;
Such details depend on your exact table structure, you should please try this out or provide more details.
You could also do:
SELECT co_ords
FROM oa
MINUS
SELECT address
FROM customers;
which can sometimes be faster than doing an anti-join. Note that MINUS does a distinct on the resultset.
I will introduce my problem with a simple example.
I have two generic queries on the same table, say table 'customers'
Defined 'plushes' a table containing information about in-store plushes, the following first query retrieves for a certain subset of Customers, say first subset, their preferred plush.
WITH preferences
AS
(
SELECT CustomerID,
CustomerName,
City,
Country,
PlushType,
PlushPrice
FROM customers cs
LEFT JOIN plushes ps
ON cs.CustomerID = ps.CustomerID
WHERE cs.CustomerID < 4
)
SELECT CustomerID, PlushType, PlushPrice
FROM preferences
In the same way, defined 'dishes' a table containing world famous dishes, the second query retrieve for a another subset of Customers, say second subset, their preferred dish.
WITH foodPreferences
AS
(
SELECT CustomerID,
CustomerName,
City,
Country,
FoodName,
FoodPrice
FROM customers cs
LEFT JOIN foods fs
ON cs.CustomerID = fs.CustomerID
WHERE fs.FoodName = 'pizza'
)
SELECT CustomerID, FoodName
FROM foodPreferences -- it returns customer 6
What I am searching for, is a query that shows customerID, plushType, plushPrice for the customers of the first OR the second subset, i.e. :
That means, I would like to apply the first query to the first OR a second (deriving from another query) subset.
In other words, I want to run the first query for those customers who love pizza.
I am using OracleDB, with PL/Sql language.
Any idea?
P.s. I know that for the written example the structure of the used queries appears weird. Indeed, I am working with something more complex and I preferred to mirror the structure of the query I have
Added this new answer that is more efficient:
with selected_customers (customerid) as (
select customerid
from customers
where customerid < 4
union
select customerid
from customers
left join foods fs on cs.customerid = fs.customerid
where fs.foodname = 'pizza'
)
select customerid, ps.plushtype, ps.plushprice
from selected_customers cs
left join plushes ps on cs.customerid = ps.customerid;
This query will do:
select customerid, plushtype, plushprice
from customers cs
left join plushes ps on cs.customerid = ps.customerid
where customerid in (
select customerid
from customers
where customerid < 4
)
or customerid in (
select customerid
from customers cs
left join foods fs on cs.customerid = fs.customerid
where fs.foodname = 'pizza'
);
I have to 2 queries below which calculate to correct value:
Select Finances.CustomerID,
sum(Finances.Total)Total
from Finances
group by Finances.CustomerID
order by Finances.CustomerID
Select Invoices.CustomerID,
sum(Invoices.InvoiceValue)InvoiceValue
from Invoices
group by Invoices.CustomerID
order by Invoices.CustomerID
within the Finances table a customer can owe money from multiple orders, so for this example lets say the customer has to pay £100+ £400 + £500, which totals to £1000.
the customer then receives the 1st invoice for £100, and pays this..
so the 2nd query would now display £100.... from these 2 values I then want to calculate a 3rd column which deducts the £100 away from the £1000 equalling £900 (the amount left to pay)
the is my table structure:
there are a lot more tables associated however this is where I am the data from with the select statements :)
how would i write the sql statement to do this all together or is it not possible? ideally i would like the to be used within a INSERT -> SELECT -> WHERE NOT EXISTS Statement or alternatively populated in a view. thanks for the help
SAMPLE DATA:
CREATE VIEW CustomerFinances AS
;WITH FinancesCTE AS
(
Select Finances.CustomerID,
sum(Finances.Total)Total
from Finances
group by Finances.CustomerID
),InvoicesCTE AS
(
Select Invoices.CustomerID,
sum(Invoices.InvoiceValue)InvoiceValue
from Invoices
group by Invoices.CustomerID
)
SELECT C.*,
F.Total AS FinanceTotal,
I.InvoiceValue
FROM Customers C
LEFT JOIN FinancesCTE F
ON C.CustomerID = F.CustomerID
LEFT JOIN InvoicesCTE I
ON C.CustomerID = I.CustomerID
GO
Try this,
CREATE VIEW CustomerFinanceDetails AS
(
select c.*,isnull(FinanceTotal,0) as FinanceTotal,isnull(InvoiceTotal,0) as InvoiceTotal
from
(select * from Customers) c
left outer join
(select CustomerID,isnull(SUM(Total),0) as FinanceTotal from Finances group by CustomerID) f on c.CustumerID=f.CustomerID
left outer join
(select CustomerID,isnull(SUM(InvoiceValue),0) as InvoiceTotal from Invoices group by CustomerID) i on c.CustumerID= i.CustomerID
)
Please note that I have seen a similar query here, but think my query is different enough to merit a separate question.
Suppose that there is a database with the following tables:
customer_table with customer_ID (key field), customer_name
orders_table with order_ID (key field), customer_ID, product_ID
Now suppose I would like to find the names of all the customers who have ordered more than 10 different types of product, and the number of types of products they ordered. Multiple orders of the same product does not count.
I think the query below should work, but have the following questions:
Is the use of count(distinct xxx) generally allowed with a "group by" statement?
Is the method I use the standard way? Does anybody have any better ideas (e.g. without involving temporary tables)?
Below is my query
select T1.customer_name, T1.customer_ID, T2.number_of_products_ordered
from customer_table T1
inner join
(
select cust.customer_ID as customer_identity, count(distinct ord.product_ID) as number_of_products_ordered
from customer_table cust
inner join order_table ord on cust.customer_ID=ord.customer_ID
group by ord.customer_ID, ord.product_ID
having count(distinct ord.product_ID) > 10
) T2
on T1.customer_ID=T2.customer_identity
order by T2.number_of_products_ordered, T1.customer_name
Isn't that what you are looking for? Seems to be a little bit simpler. Tested it on SQL Server - works fine.
SELECT customer_name, COUNT(DISTINCT product_ID) as products_count FROM customer_table
INNER JOIN orders_table ON customer_table.customer_ID = orders_table.customer_ID
GROUP BY customer_table.customer_ID, customer_name
HAVING COUNT(DISTINCT product_ID) > 10
You could do it more simply:
select
c.id,
c.cname,
count(distinct o.pid) as `uniques`
from o join c
on c.id = o.cid
group by c.id
having `uniques` > 10
I have these two tables:
Customers: Id, Name
Orders: Id, CustomerId, Time, Status
I want to get a list of customers for which the LAST order does not have a status of 'Wrong'.
I know how to use a LEFT JOIN to get a count of orders for each customer, but I don't know how I can use this statement for what I want. Maybe a JOIN is not the right thing to use too, I'm not sure.
It's possible that customers do not have any order, and they should be returned.
I'm abstracting the real tables here, but the scenario is for a windows phone app sending notifications. I want to get all clients for which their last notification does not have a 'Dropped' status. I can sort their notifications (orders) by the 'Time' field. Thanks for the help, while I continue experimenting with subqueries in the where clause.
Select ...
From Customers As C
Where Not Exists (
Select 1
From Orders As O1
Join (
Select O2.CustomerId, Max( O2.Time ) As Time
From Orders As O2
Group By O2.CustomerId
) As LastOrderTime
On LastOrderTime.CustomerId = O1.CustomerId
And LastOrderTime.Time = O1.Time
Where O1.Status = 'Dropped'
And O1.CustomerId = C.Id
)
There are obviously alternatives based on the actual database product and version. For example, in SQL Server one could use the TOP command or a CTE perhaps. However, without knowing what specific product is being used, the above solution should produce the results you want in almost any database product.
Addition
If you were using a product that supported ranking functions (which database product and version isn't mentioned) and common-table expressions, then an alternative solution might be something like so:
With RankedOrders As
(
Select O.CustomerId, O.Status
, Row_Number() Over( Partition By CustomerId Order By Time Desc ) As Rnk
From Orders As O
)
Select ...
From Customers
Where Not Exists (
Select 1
From RankedOrders As O1
Where O1.CustomerId = C.Id
And O1.Rnk = 1
And O1.Status = 'Dropped'
)
Assuming Last order refers to the Time column here is my query:
SELECT C.Id,
C.Name,
MAX(O.Time)
FROM
Customers C
INNER JOIN Orders O
ON C.Id = O.CustomerId
WHERE
O.Status != 'Wrong'
GROUP BY C.Id,
C.Name
EDIT:
Regarding your table configuration. You should really consider revising the structure to include a third table. They would look like this:
Customer
CustomerId | Name
Order
OrderId | Status | Time
CompletedOrders
CoId | CustomerId | OrderId
Now what you do is store the info about a customer or order in their respective tables ... then when an order is made you just create a CompletedOrders entry with the ids of the 2 individual records. This will allow for a 1 to Many relationship between customer and orders.
Didn't check it out, but something like this?
SELECT c.CustmerId, c.Name, MAX(o.Time)
FROM Customers c
LEFT JOIN Orders o ON o.CustomerId = c.CustomerId
WHERE o.Status <> 'Wrong'
GROUP BY c.CustomerId, C.Name
You can get list of customers with the LAST order which has status of 'Wrong' with something like
select customerId from orders where status='Wrong'
group by customerId
having time=max(time)