I have different tables with customer Id, items bought with a date of purchase.
books table consists of customer id, bookNr and date of purchase.
shoes table consists of custoemr id, shoeNr and date of purchase.
.
.
we have like for every item a table.
If the customer buys an Item(x) lets say a book with bookNr someNumber. I would like to retrieve all the orders in all the tables before the date of purchase of bookNr someNumber for all the customers.
Any suggestions how to design the query and the best way to represent the data.
The way you designed the tables mixes two concepts (type of item that got purchased and the purchase itself). This leads to the difficulties you now face.
An alternative approach would be to have a PURCHASES table that links to an "item" table. In the "item" table you could differentiate what item it is and, depending on how different the items are, link to further detail tables, that are specific to the item type.
This could be a DB design that looks like this:
[PURCHASES] -- [ITEMS] -- [BOOK_ITEM_DETAILS]
|
+-------[SHOE_ITEM_DETAILS]
If you want to keep your current design, the probably easiest approach here would be to create a view that combines (unions) the different item tables.
E.g.
CREATE view CUSTOMER_PURCHASES as
SELECT customer_id, shoe_Nr as item_nr, date_of_purchase FROM shoes
UNION ALL
SELECT customer_id, book_Nr as item_nr, date_of_purchase FROM books
...
That way, all purchases are available in a single view.
Now, if you look for all items purchased by a user before that same user bought a specific item (e.g. a shoe), you can use a join query.
SELECT customer_id, item_nr, date_of_purchase
FROM customer_purchases cp
left outer join
(SELECT customer_id, item_nr, date_of_purchase
FROM customer_purchases
where item_nr = <shoe_item_nr>
and date_of_purchase = <date_of_purchase>
and customer_id = <customer_id>) as ref_purchase
on
cp.customer_id = ref_purchase.customer_id
and cp.date_of_purchase < ref_purchase.date_of_purchase;
Related
I'm trying to build a price comparison database with n products and a definitive but changing number of vendors that sell these products.
For my price comparison database, I need to store both current prices for a product across different vendors and historical prices (one lowest price).
As I see it, I have 2 options to design the database tables:
1. Put all vendor prices into the main table.
I know how many vendors there will be and if I add or remove a vendor I can add or remove a column.
Historical prices (lowest price on certain date across all vendors), goes into a separate table with a product name, a price and a date.
2. Have one table for products and one table for prices
I will have only the static attribute data in the main table such as categories, attributes etc and then add prices to a separate product table where I store price, vendor, date in it and I can store the lowest price as a pseudo-vendor in that table for each date or I can store it in a separate table as well.
Which method would you suggest and am I missing something?
You should store the base data in a normalized format that contains all the history. This means that you have tables for:
products, with one row per product and the static information about the products.
vendors, with one row per vendor and the static information about the vendor.
prices, with one row per price along with the date and product and vendor.
You can get the current and lowest prices using a query, such as:
select pr.*
from (select pr.*, min(price) over (partition by product) as min_price
row_number() over (partition by product, vendor order by price_datetime desc) as seqnum
from prices pr
where pr.product_id = XXX
) pr
where seqnum = 1;
For performance, you want an index on prices(product, vendor, price_datetime desc).
Eventually, you may find that this query runs too slowly. In that case, you will then consider optimizations. One optimization would simply be storing the latest date for each price/vendor combination using a trigger, along with the minimum price in the products table -- presumably using triggers.
Another would be maintaining a summary table for each product and vendor using triggers. However, that is probably not how you should start the endeavor.
However, you might be surprised at how well the above query can perform on your data.
I have two tables:
A Billing table, and a Customer table.
The Billing table and customer table both share a common attribute of Customer Number.
Billing Table
I'm trying to create a view that will retrieve the customer code and bill number for the most recent invoice date. I'm having trouble ordering my query.
This is what I have so far.
CREATE VIEW RECENT_ORDER
AS
SELECT
c.Customer_Num, b.Bill_Num
FROM CUSTOMER c
INNER JOIN BILLING b ON c.Customer_Num = b.Customer_Num
WHERE c.Fname='Jess' AND c.Lname='Hanks'
HAVING MAX(b.Bill_Date);
I have also tried putting the 'HAVING' portion as a WHERE statement.
This should get your answer:
CREATE VIEW RECENT_ORDER
AS
SELECT c.customer_num, b.bill_num
FROM customer c
JOIN billing b ON c.customer_num = b.customer_num
WHERE b.bill_date =
(SELECT MAX(bill_date) FROM billing WHERE customer_num = b.customer_num)
AND c.Fname='Jess' AND c.Lname='Hanks'
Though normally I wouldn't expect to create a view that limits results to just one customer!? Remove the last line AND c.Fname ... if you intend to get the most recent result for any/all customers. Note that you may get multiple results for a customer if they have more than one invoice on the same date.
I am helping someone build a grocery deliver service. Very simple site and order process. The problem I am having is knowing how to come up with schema for the orders. The order would have contact information, but would also need to have all of the products they ordered. Since it can/will be different for each persons order, how would I go about designing this? Would I just have a products ordered field with a string list of all the items? Or would I need multiple linked tables?
Thanks!
You need three tables:
a) Products - Contains the product details
b) Orders - Contains the order header, contact information etc
c) Product_Orders - is a table with two columns: product_id and order_id, that bind the orders to the products, and a quantity field and unit price.
You could have a customers table, but ideally information like the delivery address, etc, would be attached to the order so that if the user changes his address it will not affect your order history.
For the same reason unit price must be in Product_Orders, so that if a product price changes it does not affect previous orders.
Product table
with name and price of all products.
Customer table
with name, address, phone etc...
Order table
with entries for each order: order id, cusomer id, date etc
Order Items table
with all ordered items, with link to id in ordertable, product table, quantity, price, etc...
I have two parent child tables and a couple of supporting tables. I am struggling to figure out the right relationships between them.
Orders, a table that holds a list of Orders including:Order Id, Supplier, Order Date etc..
OrderDetails, a Table holds a list of products that have been ordered, and is a child of Orders, linked on OrderId. Key fields are the ProductId and the Quantity Ordered. Each order containes one or many OrderDetails that outline the products and quantities being ordered.
Shipments, a table that holds a list of Shipments, including Tracking Number and Shipper. Links to Orders through Order Id. An Order may have multiple shipments. For example, I ordered 100 lightbulbs. They were dispatched in 5 shipments.
ShipmentDetails, holds a list of product and shipped quantities and is linked to the Shipments table by ShippingId. Each Shipment may have multiple ShipmentDetails. i.e. One shipment may have 30 Lightbulbs and 10 Door Knobs.
Products is a table that holds a list of Products that need to be both ordered and shipped.
So the logic is that I enter details about the products that are to be ordered in Products. For example, 100 CREE LED Lightbulbs, and 50 Door Handles.
When I place an order, I create an Order in Orders.
i.e. amazon.com, order #45454.
Then I add child rows to that order in OrderDetails. i.e. 30 CREE LED Lightbulbs.
When the order Ships, I create an entry in the Shipments table. i.e. Tracking #46464646464, linked to OrderId in Orders. And then I enter what is in that shipment in ShipmentDetails. For example, only 20 or the 30 CREE LED Lightbulbs may be associated with this Shipping entry.
I am struggling with figuring out how to relate the Shipping Detail records to the Order Detail Table. Lets say the Shipping Detail Table has 4 fields.
ShippingID - a link to the Shipments table parent.
TrackingNum - a field that holds a tracking number.
Product - this should be a drop down, that says, the shipment I belong to is related to a defined Order (because ShipmentDetail is a child of a Shipment record which in turn holds a key to the Orders table, which in turn has OrderDetails that reference products).
Quantity - this should have a default (overridable) value that is the "Quantity Ordered" number from the OrdersDetail record that matches the Order Id and Product Id. Where OrderId is in the Shipments table (linked to the Orders table) and ProductID comes from #3 above. The reason it must be overridable is that a shipment may be a partial shipment.
I am stuck with the preceding #3 and #4. I hope I have explained this in a vaguely understandable way! The pictures below may help!
The ask:
What is the correct join between the ShipmentDetails and the OrderDetail Table
How do I create a field in the ShipmentDetail table with a default value pulled from the Quantities Field of the OrderDetail table, where
Shipments!OrderId = Orders!Id and ShipmentDetail!ProductID = OrderDetails!Product ID
I am working in MS Access 2016 - but I suspect this is a fairly generic SQL question...rather than MS Access specific.
I think the naming is confusing.
What I would rather have is (each first id is autoincrement, forgot how to say this on access):
// Product doesn't contain any information about quantity/price etc ...
create table Products(product_id int, name text, description text ...);
// Orders:
create table Orders(order_id int, client_name text, description text ...);
create table OrderDetails(order_detail_id int, order_id int, product_id int, quantity double, unit_price double, ...);
// Shipments
create table Shipments(shipment_id int, company text, description text ...);
create table ShipmentDetails(shipment_detail_id int, shipment_id int, product_id int, quantity double, price double default 0, ...);
// inserting shipments per product (defaulting to total quantity per product), assuming we have shipment_id SID
insert into ShipmentDetails(shipment_id, order_id, product_id, quantity)
select SID, order_id, product_id, SUM(quantity)
from OrderDetails
group by order_id, product_id;
Then you can of course have some filters (date, customer etc ...).
For the first question, I am not clear what exaclty you want to return.
Here is a comparison of quantities:
select t.order_id, t.product_id, sum(t.quantity) as product_quantity, sum(u.quantity) as shipment_quantity
from OrderDetails t inner join ShipmentDetails u
on t.order_id = u.order_id and t.product_id = u.product_id;
I have a large table of orders with 20+ columns. Within this there are ACCOUNT_ID and PAYMENT_TYPE.
I'd like to have three separate tables, based on preferred (most common) payment type.
I can count the payment type for each client easily enough, but have no idea as to the logic behind achieving what I need.
Hoping someone can point me int he right direction?
Please let me know if this is not clear, or an example is needed
Assuming you wanted the tables split as different payment types, use views and not separate tables or each time you insert a row into Orders, you need to also insert into the relevant Order[PaymentType] table through some mechanism (manually, trigger etc).
As W3schools puts it:
In SQL, a view is a virtual table based on the result-set of an SQL
statement.
You define a query that returns a result set, then you can treat that like you would a table. This means as you insert rows into Orders, you can view them in your view if they match the conditions, you do not need to worry about updating another table.
Assuming you wish to split them on payment types, and you had a similar payment type table as the following:
PaymentTypeId PaymentTypeDesc
----------------------------------
1 Cash
2 Cheque
3 Credit Card
then the following might be what you're looking for.
CREATE VIEW vw_OrdersCash AS
SELECT *
FROM Orders
WHERE PAYMENT_TYPE = 1
CREATE VIEW vw_OrdersCheque AS
SELECT *
FROM Orders
WHERE PAYMENT_TYPE = 2
CREATE VIEW vw_OrdersCreditCard AS
SELECT *
FROM Orders
WHERE PAYMENT_TYPE = 3
Just treat them as tables to do whatever you wish.
SELECT * FROM vw_OrdersCash
EDIT:
Reading one of your comments to your question, it sounds like you want it more dynamic than the suggestion above. It's hard to tell without sample output what it is you're trying to achieve, but if you wanted 3 dynamic tables you could extend the above, and rather than the views filtering to a specific payment type, they would filter to the 1st, 2nd and 3rd most common at the time of execution.
An idea of how to do this is below. The lookup view vw_OrdersTopThreePaymentMethods looks at the orders table and returns the top three payment types in descending order of number of orders (ie 1st, 2nd, 3rd). There are then views that will grab all of the orders on that specific type, with all the order information available for you to query as you want.
-- A lookup view that returns the top 3 payment methods of orders
CREATE VIEW vw_OrdersTopThreePaymentMethods AS
SELECT TOP 3
ROW_NUMBER() OVER(ORDER BY a.OrderCount DESC) AS Row,
PAYMENT_TYPE,
OrderCount
FROM (
SELECT PAYMENT_TYPE , COUNT(*) as 'OrderCount'
FROM Orders
GROUP BY PAYMENT_TYPE
) a
ORDER BY a.OrderCount desc
-- 3 views that then get the orders for the top three methods based on output of vw_OrdersTopThreePaymentMethods
CREATE VIEW vw_OrdersPrimaryPayment AS
SELECT *
FROM Orders
WHERE PAYMENT_TYPE IN (
SELECT PAYMENT_TYPE
FROM vw_OrdersTopThreePaymentMethods
WHERE Row = 1
)
CREATE VIEW vw_OrdersSecondaryPayment AS
SELECT *
FROM Orders
WHERE PAYMENT_TYPE IN (
SELECT PAYMENT_TYPE
FROM vw_OrdersTopThreePaymentMethods
WHERE Row = 2
)
CREATE VIEW vw_OrdersTertiaryPayment AS
SELECT *
FROM Orders
WHERE PAYMENT_TYPE IN (
SELECT PAYMENT_TYPE
FROM vw_OrdersTopThreePaymentMethods
WHERE Row = 3
)