复杂的 Oracle SQL 查询

Question

I started learning SQL a few weeks back on my own and came upon an interesting problem that I can't seem to solve. Here's the database structure:

Material (name, price, origin_country) 
Product (name, price) 
Quantities (productName, materialName, quantity)

The query should show all data of the Material that's being used in the most Products that cost 20.000 or less .

This is what I have so far:

select max(count(m.name))
from Materials m
join Quantities q on (m.name=q.materialName)
join Product p on (p.name=q.productName)
where p.price < 20000
group by m.name

This, in theory, should show show the maximum number that a type of material appears in (and it indeed does so in practice). The problem is, I have no idea how to implement this in a way that it can show me the data from the Material table.

Answer 1

Join the tables together, filter out the products that are too expensive and then use the COUNT analytic function to find the number of products and ORDER BY that count in descending order and return the FIRST ROW WITH TIES :

SELECT M.*,
       P.name AS ProductName,
       p.Price,
       Q.Quantity,
       COUNT( DISTINCT p.ROWID ) OVER ( PARTITION BY m.ROWID ) AS num_products
FROM   Material M
       INNER JOIN Quantities Q
       ON ( m.Name = Q.MaterialName )
       INNER JOIN Product P
       ON ( Q.ProductName = P.Name )
WHERE  p.price <= 20000
ORDER BY num_products DESC
FETCH FIRST ROW WITH TIES;

(I used the ROWID pseudo-column in the count just in-case there were two products or materials with the same name then it would not group them together. If this is not going to be the case then you can just use p.Name and m.Name instead.)

Which, for the sample data:

CREATE TABLE Material( name, price, origin_country ) AS
SELECT 'M1', 1, 'Place1' FROM DUAL UNION ALL
SELECT 'M2', 2, 'Place2' FROM DUAL UNION ALL
SELECT 'M3', 3, 'Place3' FROM DUAL;

CREATE TABLE Product (name, price) AS
SELECT 'P123', 10 FROM DUAL UNION ALL
SELECT 'P13',   8 FROM DUAL UNION ALL
SELECT 'P223',  5 FROM DUAL;

CREATE TABLE Quantities (productName, materialName, quantity) AS
SELECT 'P123', 'M1', 1 FROM DUAL UNION ALL
SELECT 'P123', 'M2', 1 FROM DUAL UNION ALL
SELECT 'P123', 'M3', 1 FROM DUAL UNION ALL
SELECT 'P13',  'M1', 1 FROM DUAL UNION ALL
SELECT 'P13',  'M3', 1 FROM DUAL UNION ALL
SELECT 'P223', 'M2', 1 FROM DUAL UNION ALL
SELECT 'P223', 'M2', 1 FROM DUAL UNION ALL
SELECT 'P223', 'M3', 1 FROM DUAL;

Outputs:

\nNAME | PRICE | ORIGIN_COUNTRY |  PRODUCTNAME | PRICE | QUANTITY | NUM_PRODUCTS \n:--- |  ----: |  :------------- |  :---------- |  ----: |  -------: |  -----------: \nM3 |  3 |  Place3 | P123 |  10 |  1 |  3 \nM3 |  3 |  Place3 | P223 |  5 |  1 |  3 \nM3 |  3 |  Place3 | P13 |  8 |  1 |  3 \n

db<>fiddle here