Sql 查询从多个表中获取多个数据

Question

Given the following tables:

• Clients (ClientId, Name, Surname, Age)

• Products (ProductId, Name, Price)

• Purchases (Purchaseld, Date, ClientId, Productid)

I need to write an SQL query that shows the quantity of purchases made by clients. It must only show the clients who made more than 1 purchase. The result should contain the following fields: Full name (ie "john rambo"), Quantity of purchases.

I have written this query but results are not coming correct

SELECT Concat(clients.name, clients.surname) 
FROM   clients 
       JOIN products 
         ON clients.name = products.name 
       JOIN purchases 
         ON products.productid = purchases.productid 
GROUP  BY clientid 
HAVING Count(clientid) > 1 

Answer 1

SELECT Concat(clients.name, ' ', clients.surname),
       count(*) as number_of_orders
FROM   clients 
       JOIN purchases 
         ON products.productid = purchases.productid 
GROUP  BY Concat(clients.name, ' ', clients.surname) 
HAVING Count(clientid) > 1 

As noted in the comments, your join to products doesn't make much sense - your asking to only return records where there's a product that matches a client's first name.

CONCAT will glue the two fields together (eg "JohnRambo")

Answer 2

It must only show the clients who made more than 1 purchase.

Your question has no mention of products, so there is no need for that in the query:

SELECT CONCAT(c.name, c.surname) 
FROM clients c JOIN
     purchases p
     ON p.ClientId = c.ClientId 
GROUP  BY c.ClientId, CONCAT(c.name, c.surname) 
HAVING COUNT(*) > 1 ;

Note that the ClientId presumably uniquely defines the clients -- not the names. So the ClientId should be part of the aggregation.