Comment sélectionner le résultat souhaité dans MySQL?

Question

configuration:

create table main(id integer unsigned);  
create table test(id integer unsigned,created datetime,text text); 

insert into main value(1); 
insert into test value(1,now(),'something1');  
insert into test value(1,now() + interval 1 day,'something2'); 

utilisant:

select main.id, text from main left join test on main.id=test.id 
group by main.id where main.id in (1,2,3); 

retours:

+------+------------+ 
| id | text  | 
+------+------------+ 
| 1 | something1 | 
+------+------------+ 

Comment obtenir

+------+------------+ 
| id | text  | 
+------+------------+ 
| 1 | something2 | 
+------+------------+ 

Answer 1

Essayez l'instruction SQL suivante:

SELECT id, (
    SELECT text 
    FROM test 
    WHERE test.ID = main.ID 
    ORDER BY created DESC 
    LIMIT 0 , 1 
    ) AS text 

FROM main 

Edit:

Dans le cas où vous avez besoin de plusieurs colonnes de test de la table, vous devez ajouter une clé primaire. Ensuite, dans votre requête, d'abord obtenir la colonne de clé primaire et de l'utiliser comme référence sur les sous-requêtes suivantes:

# Add the primary key 
ALTER TABLE `test` ADD `test_id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY FIRST ; 

# Select many columns 
SELECT id, (

    SELECT test_id 
    FROM test 
    WHERE test.ID = main.ID 
    ORDER BY created DESC 
    LIMIT 0 , 1 

) AS testID, (

    SELECT text 
    FROM test 
    WHERE test_id = testID 

) AS text, (

    SELECT created 
    FROM test 
    WHERE test_id = testID 

) AS created 

FROM main 

Answer 2

select id, text from main left join test on main.id=test.id order by created 

Vous devrez peut-être utiliser ASC (fin) ou DESC (fin)

Answer 3

ÉDITÉE:

Qu'en est-ce?

select 
    main.id, a1.created,a1.text 
from 
    main 
inner join test a1 on 
    a1.id = main.id 
LEFT OUTER JOIN test a2 ON 
    (a1.id = a2.id 
    AND (a1.created < a2.created)) 
WHERE a2.id IS NULL; 

Answer 4

SELECT 
     main.id , test.created , test.text 
    FROM 
     main 
     JOIN test ON (main.id = test.id) 
     JOIN (select id,max(created) as created from test group by id) as t2 ON (test.id = t2.id and test.created =t2.created)