Question

设置：

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');

使用：

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);

返回：

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

如何获得

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

Answer 1

尝试以下SQL语句：

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

FROM main

编辑：

如果您需要表测试中的多个列，则需要添加主键。然后，在您的查询中，首先获取主键列并将其用作以下子查询的参考：

# 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

已编辑：

这个怎么样？

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 3

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)

Answer 4

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

您可能需要使用ASC（结束）或DESC（结束）

如何在MySQL中选择所需的结果？

4 个答案: