I am struggling with a sql statement. I am hoping a guru can help a beginner out, currently I have multiple select in statements.. but think there is a better way as I have been stuck.
Below are the tables and pertinent columns in each table
country
-country_id
barcodes_banned_in_country
-barcode(varchar)
-country_id
-country_name
orders
-order_id
-country_name
item
-order_id
-item_id
-barcode(varchar)
The goal is to get all orders that are banned based off the barcode banned list.
Any help with this sql statement would be appreciated.
One option uses exists:
select o.*
from orders o
where exists (
select 1
from barcodes_banned_in_country bic
inner join item i on i.barcode = bic.barcode
where i.order_id = o.order_id and bic.country_name = o.country_name
)
This brings all orders whose at least one item have a barcode that is banned in the order's country.
If, on the other hand, you want the list of the banned barcodes per order, then you can join and aggregate:
select o.order_id, o.country_name, listagg(i.barcode, ',') banned_barcodes
from orders o
inner join item i
on i.order_id = o.order_id
inner join barcodes_banned_in_country bic
on i.barcode = bic.barcode
and bic.country_name = o.country_name
group by o.order_id, o.country_name
Note that, as commented by MT0, you should really be storing the id of the country in orders rather than the country name. Accordingly, you wouldn't need the country name in the banned barcodes table.
Related
I have a table of orders, and a table of products contained in these orders. (The products-table has order_id, a foreign key referring to orders.id).
I would like to query the number of products contained in each order. However, I also want orders to be contained in the results if they do not contain any products at all.
This means that a simple
SELECT *, COUNT(*) n_products FROM `orders` INNER JOIN `products` on `products.order_id` = `orders.id` GROUP_BY `order_id`
does not work, since orders without any products disappear.
Using a LEFT OUTER JOIN instead would add rows without product-information, but the distinction between an order with 1 product and an order with 0 products is lost.
What am I missing here?
You need a left join here, and you should be counting some column from the products table:
SELECT
o.*,
COUNT(p.order_id) AS n_products
FROM orders o
LEFT JOIN products p
ON p.order_id = o.id
GROUP BY
o.id;
Note that I assume that Postgres would allow grouping by orders.id and then selecting all columns from that table. If not, then you would only be able to select o.id in addition to the count.
EDIT: Added the query I came up with.
I'm a beginner at SQL (having it be taught as part of a database management class I am currently taking). One of my projects is to create a database revolving around customers and their orders. For this project, I have to make four tables:
Customer (PK = CustomerID),
Invoice (PK = InvoiceID/ FK = CustomerID),
Product (PK = ProductSKU), and
Invoice_Item (PK = FK Invoice ID + FK ProductSKU).
I have to make a query that asks the question of "What customers have ordered more than 3 of a certain item?" The query contains the fields of the CustomerID (C_ID), CustomerName (C_BUS), InvoiceID (I_NUM), ProductSKU (P_SKU), and ProductAmountOrdered (II_ORDERED) (attribute of the Invoice_Item table). Also note that the Invoice_ID and ProductSKU attributes in the query are coming from the Invoice_Item table. Now, I answered the question with the help of some joins, but there is a catch. The customer still satisfies the criteria if they have ordered more than 3 items across multiple orders (say they order 2 in one order and 2 in another). This is the part that is tripping me up. What is the best way to go about doing this? I have looked around and haven't found anything that seems like it would solve this question. Any help wold be greatly appreciated!
Here is the code that I have so far:
SELECT CUSTOMER.C_ID, C_BUS, P_SKU, INVOICE.I_NUM, INVOICE_ITEM.II_ORDERED
FROM CUSTOMER, INVOICE, INVOICE_ITEM
WHERE CUSTOMER.C_ID = INVOICE.C_ID
AND INVOICE.I_NUM = INVOICE_ITEM.I_NUM
AND INVOICE_ITEM.P_SKU = 'P0548'
AND II_ORDERED > 3
ORDER BY C_BUS DESC;
I understand that this might not be the best syntax, but this is what I managed using my textbook as a reference.
Please modify the queries as per your naming standards.
query for the customers who ordered more then three of a certain item across all their invoices:
select c.customer_id,
c.customer_name,
ii.product_sku,
sum(ii.ProductAmountOrdered)
as total_quantity_ordered
from customer c
inner join invoice i on c.customer_id = i.customer_id
inner join invoice_item ii on i.invoice_id = ii.invoice_id
group by c.customer_id,
c.customer_name,
ii.product_sku
having sum(ii.ProductAmountOrdered) >= 3;
Query to fetch customers that ordered more then 3 of a product in a single order/invoice:
select c.customer_id,
c.customer_name,
ii.invoice_id,
ii.product_sku,
sum(ii.ProductAmountOrdered)
as total_quantity_ordered
from customer c
inner join invoice i on c.customer_id = i.customer_id
inner join invoice_item ii on i.invoice_id = ii.invoice_id
group by c.customer_id,
c.customer_name,
ii.invoice_id,
ii.product_sku
having sum(ii.ProductAmountOrdered) >= 3;
I am trying to work out how to go about this one SQL query.
I have two tables Orders and Customers.
Orders has two columns CustomerNumber and Fruit
Customers has two columns as well CustomerNumber and Address
Not all customers have placed an order but I need a query that runs through the list of Customers.CustomerNumber and lists how many times that Customers.CustomerNumber times shows up in the table Orders.
It's a countif query but im not sure how to set it up.
select customer.id, count(order.*)
from Customer inner join Order on Customer.id=Order.ID
group by customer.id
select c.CustomerNumber, count(1)
from Customer as c
left join Order as o on c.CustomerNumber = o.CustomerNumber
group by c.CustomerNumber
This will return a zero for customer's without any orders.
I'm taking my first steps in terms of practical SQL use in real life.
I have a few tables with contractual and financial information and the query works exactly as I need - to a certain point. It looks more or less like that:
SELECT /some columns/ from CONTRACTS
Linked 3 extra tables with INNER JOIN to add things like department names, product information etc. This all works but they all have simplish one-to-one relationship (one contract related to single department in Department table, one product information entry in the corresponding table etc).
Now this is my challenge:
I also need to add contract invoicing information doing something like:
inner join INVOICES on CONTRACTS.contnoC = INVOICES.contnoI
(and selecting also the Invoice number linked to the Contract number, although that's partly optional)
The problem I'm facing is that unlike with other tables where there's always one-to-one relationship when joining tables, INVOICES table can have multiple (or none at all) entries that correspond to a single contract no. The result is that I will get multiple query results for a single contract no (with different invoice numbers presented), needlessly crowding the query results.
Essentially I'm looking to add INVOICES table to a query to just identify if the contract no is present in the INVOICES table (contract has been invoiced or not). Invoice number itself could be presented (it is with INNER JOIN), however it's not critical as long it's somehow marked. Invoice number fields remains blank in the result with the INNER JOIN function, which is also necessary (i.e. to have the row presented even if the match is not found in INVOICES table).
SELECT DISTINCT would look to do what I need, but I seemed to face the problem that I need to levy DISTINCT criteria only for column representing contract numbers, NOT any other column (there can be same values presented, but all those should be presented).
Unfortunately I'm not totally aware of what database system I am using.
Seems like the question is still getting some attention and in an effort to provide some explanation here are a few techniques.
If you just want any contract with details from the 1 to 1 tables you can do it similarily to what you have described. the key being NOT to include any column from Invoices table in the column list.
SELECT
DISTINCT Contract, Department, ProductId .....(nothing from Invoices Table!!!)
FROM
Contracts c
INNER JOIN Departments D
ON c.departmentId = d.Department
INNER JOIN Product p
ON c.ProductId = p.ProductId
INNER JOIN Invoices i
ON c.contnoC = i.contnoI
Perhaps a Little cleaner would be to use IN or EXISTS like so:
SELECT
Contract, Department, ProductId .....(nothing from Invoices Table!!!)
FROM
Contracts c
INNER JOIN Departments D
ON c.departmentId = d.Department
INNER JOIN Product p
ON c.ProductId = p.ProductId
WHERE
EXISTS (SELECT 1 FROM Invoices i WHERE i.contnoI = c.contnoC )
SELECT
Contract, Department, ProductId .....(nothing from Invoices Table!!!)
FROM
Contracts c
INNER JOIN Departments D
ON c.departmentId = d.Department
INNER JOIN Product p
ON c.ProductId = p.ProductId
WHERE
contnoC IN (SELECT contnoI FROM Invoices)
Don't use IN if the SELECT ... list can return a NULL!!!
If you Actually want all of the contracts and just know if a contract has been invoiced you can use aggregation and a case expression:
SELECT
Contract, Department, ProductId, CASE WHEN COUNT(i.contnoI) = 0 THEN 0 ELSE 1 END as Invoiced
FROM
Contracts c
INNER JOIN Departments D
ON c.departmentId = d.Department
INNER JOIN Product p
ON c.ProductId = p.ProductId
LEFT JOIN Invoices i
ON c.contnoC = i.contnoI
GROUP BY
Contract, Department, ProductId
Then if you actually want to return details about a particular invoice you can use a technique similar to that of cybercentic87 if your RDBMS supports or you could use a calculated column with TOP or LIMIT depending on your system.
SELECT
Contract, Department, ProductId, (SELECT TOP 1 InvoiceNo FROM invoices i WHERE c.contnoC = i.contnoI ORDER BY CreateDate DESC) as LastestInvoiceNo
FROM
Contracts c
INNER JOIN Departments D
ON c.departmentId = d.Department
INNER JOIN Product p
ON c.ProductId = p.ProductId
GROUP BY
Contract, Department, ProductId
I would do it this way:
with mainquery as(
<<here goes you main query>>
),
invoices_rn as(
select *,
ROW_NUMBER() OVER (PARTITION BY contnoI order by
<<some column to decide which invoice you want to take eg. date>>) as rn
)
invoices as (
select * from invoices_rn where rn = 1
)
select * from mainquery
left join invoices i on contnoC = i.contnoI
This gives you an ability to get all of the invoice details to your query, also it gives you full control of which invoice you want see in your main query. Please read more about CTEs; they are pretty handy and much easier to understand / read than nested selects.
I still don't know what database you are using. If ROW_NUMBER is not available, I will figure out something else :)
Also with a left join you should use COALESCE function for example:
COALESCE(i.invoice_number,'0')
Of course this gives you some more possibilities, you could for example in your main select do:
CASE WHEN i.invoicenumber is null then 'NOT INVOICED'
else 'INVOICED'
END as isInvoiced
You can use
SELECT ..., invoiced = 'YES' ... where exists ...
union
SELECT ..., invoiced = 'NO' ... where not exists ...
or you can use a column like "invoiced" with a subquery into invoices to set it's value depending on whether you get a hit or not
Im practicing basic SQL with this site http://www.sqlishard.com/Exercise
Here is the question:
S5.0 - INNER JOIN
Now that we can pull data out of a single table and qualify column
names, let's take it a step further. JOIN statements allow us to
'join' the rows of several tables together using a condition to define
how they match one another. SELECT [columns] FROM FirstTable INNER
JOIN SecondTable ON FirstTable.Id = SecondTable.FirstTableId
Try using the INNER JOIN syntax to SELECT all columns from the
Customers and Orders tables where the CustomerId column in Orders
matches the Id column in Customers. Since both tables have an Id
column, you will need to qualify the Customers id in the WHERE clause
with either the table name or a table alias.
Here is my answer:
SELECT *
FROM Customers AS c
INNER JOIN Orders AS o ON c.ID = o.ID
WHERE o.CustomerID = c.ID
The site says im wrong? Could anyone explain where i'm going wrong?
EDIT: I see now I dont need the WHERE clause, but the question states..
you will need to qualify the Customers id in the WHERE clause with
either the table name or a table alias.
Hence my confusion. Thanks none the less.
Try this way:
SELECT c.ID,o.ID
FROM Customers AS c
INNER JOIN Orders AS o ON o.CustomerID = c.ID
or using where clause
SELECT *
FROM Customers AS c, Orders AS o
where o.CustomerID = c.ID
If you use JOIN.. ON, you do not need where clause