什么Mysql查询将返回此结果？

Question

我有两个A,B相互关联的表(简化):

A:
+-------+---------+ 
| id    | type    | 
+-------+---------+ 
| 1     | apple   | 
| 2     | orange  | 
| 3     | banana  | 
+-------+---------+ 

B:
+-------+---------+-----------+ 
| id    | a_id    |  rank     |  
+-------+---------+-----------+  
| 1     | 1       |  9.9      |
| 2     | 1       |  7.7      |
| 3     | 2       |  3.3      |
| 4     | 2       |  8.8      |
| 5     | 2       |  1.1      |  
| 6     | 3       |  3.3      |
| 7     | 3       |  2.2      | 
| 8     | 1       |  0.0      | 
+-------+---------+-----------+   

什么mysql查询将返回以下结果？

Result
+-------+---------+-----------+ 
| id    | type    |  rank     |  
+-------+---------+-----------+  
| 1     | apple   |  0.0      | 
| 2     | orange  |  1.1      | 
| 3     | banana  |  2.2      | 
+-------+---------+-----------+ 

选择在表B中最后插入的等级(它不是 MAX(等级)).

需要从具有最高id的表B中选择结果表中的排名.

Answer 1

更新

你可能想尝试使用子查询加盟,以获得MAX(id)每个a_id中table_b,然后INNER JOIN用table_b获得的排名:

SELECT   ta.id, 
         ta.type,
         tb.rank
FROM     table_a ta
JOIN     (
            SELECT   MAX(id) AS id, 
                     a_id
            FROM     table_b
            GROUP BY a_id
         ) sub_q ON (sub_q.a_id = ta.id)
JOIN     table_b tb ON (tb.id = sub_q.id)
ORDER BY ta.id;

测试用例:

CREATE TABLE table_a (id int, type varchar(10));
CREATE TABLE table_b (id int, a_id int, rank decimal(2,1));

INSERT INTO table_a VALUES (1, 'apple');
INSERT INTO table_a VALUES (2, 'orange');
INSERT INTO table_a VALUES (3, 'banana');

INSERT INTO table_b VALUES (1, 1, 9.9);      
INSERT INTO table_b VALUES (2, 1, 7.7);       
INSERT INTO table_b VALUES (3, 2, 3.3);       
INSERT INTO table_b VALUES (4, 2, 8.8);      
INSERT INTO table_b VALUES (5, 2, 1.1);         
INSERT INTO table_b VALUES (6, 3, 3.3);       
INSERT INTO table_b VALUES (7, 3, 2.2);       
INSERT INTO table_b VALUES (8, 1, 0.0);      

结果:

+------+--------+------+
| id   | type   | rank |
+------+--------+------+
|    1 | apple  |  0.0 |
|    2 | orange |  1.1 |
|    3 | banana |  2.2 |
+------+--------+------+
3 rows in set (0.01 sec)