SQL Server：选择表中与其他表中的行共享值的行

Question

I have searched the questions but haven't been able to find an answer. Perhaps my wording may be wrong. My problem is as follows:

Given table Users :

ID      code       owner
 1       777       James
 2       432      George
 3       111        Kale

And table Products :

ID      product_name        code
 1             chair         777
 2             table         777
 3               fan         432
 4           monitor         777
 5              sofa         111
 6               bed         111

I need a query that fetches N number of rows from table Users and then fetches all rows from table Products that have a code matching the code of Any row fetched previously.

Is this possible in SQL Server? Is it optimal?

For above example if i fetch first 2 rows (owners James and George) I should get all products with code 777 and 432.

Answer 1

Yes it is a common thing, called "Joins"

for example this would give you the answer:

Select products.product_name,users.owner FROM products LEFT JOIN users ON products.code=users.code

You can read more about JOINS here: https://www.w3schools.com/sql/sql_join.asp

Answer 2

To select the first n (here 2 ) users use TOP . Put that in a subquery and LEFT JOIN products on the common code to it.

SELECT *
       FROM (SELECT TOP 2
                    *
                    FROM users
                    ORDER BY id) u
            LEFT JOIN products p
                      ON p.code = u.code;

If you want to make users, that don't have at least one product, disappear you can replace the LEFT JOIN by an INNER JOIN .

Answer 3

Try this with Inner join :

Select products.product_name,users.owner FROM products inner JOIN users ON products.code=users.code
where users.code in (777,432)

Answer 4

Create table #Users
(
    Id int Identity(1,1),
    Code varchar(100),
    Owner varchar(100)
)

Create table #Products
(
    Id int Identity(1,1),
    ProductName varchar(100),
    Code varchar(100)
)


insert Into #Users(Code,Owner)
Select '777','James'


insert Into #Users(Code,Owner)
Select '432','George'

insert Into #Users(Code,Owner)
Select '111','Kale'


insert Into #Products(ProductName,Code)
Select 'Chair','777'

insert Into #Products(ProductName,Code)
Select 'Table','777'

insert Into #Products(ProductName,Code)
Select 'fan','432'

insert Into #Products(ProductName,Code)
Select 'monitor','777'

insert Into #Products(ProductName,Code)
Select 'Sofa','111'

insert Into #Products(ProductName,Code)
Select 'bed','111'

select * from #products


select * from #Products Left join #Users on #Users.Code=#Products.Code Where Owner in ('James','George')

Answer 5

This works even if code is not unique;

select * from Products where code in
 (
  select top 2 code from users order by id
 )

Replace 2 with the relevant N