Get First Row of SubQuery - sql

Question

I have a table with clients and I need to show the first country of each client like a default country.
Table Clients
ID_Client | Name_Client
1 | Mike
2 | Jon
3 | Ben
Table Countries
ID_Country | ID_Client | Name_Country
1 | 1 | France
2 | 1 | USA
3 | 1 | England
4 | 2 | Portugal
5 | 2 | Spain
6 | 3 | Germany
I only want the first row of each country.
Example:
Mike - France
Jon - Portugal
Ben - Germany
I tried this but only retry 1 row:
SELECT Name_Client, Name_Country
FROM Clients
WHERE ID_Client =
(SELECT TOP 1 ID_Client
From Countries
order by ID_Country)
Result:
Mike | France

Answer 1

Your sub-query isn't correlated, try to use APPLY :
SELECT c.Name_Client, cn.Name_Country
FROM Clients C OUTER APPLY
(SELECT TOP (1) cn.Name_Country
From Countries CN
WHERE cn.ID_Client = c.ID_Client
ORDER BY cn.ID_Country
) cn;

Answer 2

You can use Outer APPLY or CROSS APPLY as per Below example,
SELECT C.Name_Client + ' - ' + V.Name_Country
FROM Clients C
OUTER APPLY(
SELECT TOP 1 * FROM Countries CO WHERE CO.ID_Client = C.ID_Client
ORDER BY ID_Country
) V

Answer 3

SQL Fiddle
MS SQL Server 2017 Schema Setup:
CREATE TABLE CLIENTS (ID_Client int,Name_Client varchar(255))
CREATE TABLE COUNTRIES(ID_Country int,ID_Client int,Name_Country varchar(255))
INSERT INTO CLIENTS(ID_Client,Name_Client)VALUES(1,'Mike'),(2,'Jon'),(3,'Ben')
INSERT INTO COUNTRIES(ID_Country,ID_Client,Name_Country)VALUES(1,1,'France'),
(2,1,'USA'),(3,1,'England'),
(4,2,'Portugal'),(5,2,'Spain'),
(6,3,'Germany')
Query 1:
with CTE as
( select c.Name_Client, ct.Name_Country,
row_number() over(partition by c.ID_Client order by ct.ID_Country) as rn
FROM CLIENTS c
left join COUNTRIES ct on c.ID_Client=ct.ID_Client
)
select CTE.Name_Client,CTE.Name_Country from CTE where rn=1
Results:
| Name_Client | Name_Country |
|-------------|--------------|
| Mike | France |
| Jon | Portugal |
| Ben | Germany |

Answer 4

Rather than having a nested query like this try this instead.
SELECT clients.Name_Client, countries.Name_Country
FROM Clients clients
LEFT JOIN Countries countries on countries.ID_Client = clients.ID_Client
By performing the join you are matching the record and not having a subquery go off and get a bucket load of bad data.

Answer 5

use row_number()
with cte as
( select c.Name_Client, cn.Name_Country,
row_number() over(partition by c.ID_Client order by ID_Country) rn clients c join country cn on c.client_id=cn.client_id
) select * form cte where rn=1

Answer 6

You can use common table expression and filter on the row number partitioned by the id_client. Like this the row_number is incremented until a new id_client is found.
WITH cte_countries AS(
SELECT ROW_NUMBER() OVER (PARTITION BY ID_Client ORDER BY ID_Client) AS Row#,
Countries.*
FROM Countries)
SELECT * FROM Clients cli
JOIN cte_countries coun ON cli.ID_Client = coun.ID_Client
WHERE coun.Row# = 1

Answer 7

You can try this
SELECT * FROM (
SELECT Name_Client, Name_Country ,
RwNumbr = ROW_NUMBER() OVER(PARTITION by c.ID_Client order by cl.ID_Country)
from CLIENTS c
JOIN COUNTRIES cl
ON cl.ID_Client = c.ID_Client
) as f
WHERE f.RwNumbr = 1