我怎样才能 select 具有相同值的记录？

Question

I have a table. This table includes customers and products. Sample data is is in below.

Customer Name	Product
John	laptop
John	telephone
John	laptop
Kevin	laptop
Kevin	laptop
Kevin	laptop

I want to select customer who chose all their products with a laptop so This case I want to select Kevin because he selected laptop his all products. I dont want to select john because he selected laptop but also select telephone not all product of john laptop.

How can I do this in tsql?

Answer 1

You can use conditional aggregation in the having clause

SELECT [Customer Name]
FROM YourTable t
GROUP BY [Customer Name]
HAVING COUNT(CASE WHEN Product <> 'laptop' THEN 1 END) = 0
-- alternatively
HAVING COUNT(CASE WHEN Product = 'laptop' THEN 1 END) = COUNT(*)

Answer 2

SELECT Name
FROM Customers
WHERE (SELECT Name FROM Customers WHERE Product = 'telephone') != Name
GROUP BY NAME;

This should help you, it might not be the final asnwer but it shall provide enough for you to figure it out in some edge cases