MySQL仅加入最近一行？

Question

我有一个表顾客存储customer_id，电子邮件和参考。还有一个额外的表customer_data，用于存储对客户进行的更改的历史记录，即插入新行时发生更改。

为了在表中显示客户信息，需要连接两个表，但只有customer_data中最近的一行应该连接到customer表。

由于查询是分页的，所以有一个限制和一个偏移量。

我该怎么用MySQL做到这一点？我想我希望把不同之处在那里的某个地方......

在一分钟的查询就像是这个 -

SELECT *, CONCAT(title,' ',forename,' ',surname) AS name 
FROM customer c 
INNER JOIN customer_data d on c.customer_id=d.customer_id 
WHERE name LIKE '%Smith%' LIMIT 10, 20 

Additionaly，我是正确的思维，我可以在使用CONCAT与LIKE这条路？

（我明白，INNER JOIN可能是错误的连接类型使用的。其实，我不知道有什么区别之间的不同连接。我要去看看现在！）

Answer 1

你可能想尝试以下操作：

SELECT CONCAT(title, ' ', forename, ' ', surname) AS name 
FROM  customer c 
JOIN  (
       SELECT MAX(id) max_id, customer_id 
       FROM  customer_data 
       GROUP BY customer_id 
     ) c_max ON (c_max.customer_id = c.customer_id) 
JOIN  customer_data cd ON (cd.id = c_max.max_id) 
WHERE  CONCAT(title, ' ', forename, ' ', surname) LIKE '%Smith%' 
LIMIT  10, 20; 

注意，一个JOIN仅仅是INNER JOIN的代名词。

测试用例：

CREATE TABLE customer (customer_id int); 
CREATE TABLE customer_data (
    id int, 
    customer_id int, 
    title varchar(10), 
    forename varchar(10), 
    surname varchar(10) 
); 

INSERT INTO customer VALUES (1); 
INSERT INTO customer VALUES (2); 
INSERT INTO customer VALUES (3); 

INSERT INTO customer_data VALUES (1, 1, 'Mr', 'Bobby', 'Smith'); 
INSERT INTO customer_data VALUES (2, 1, 'Mr', 'Bob', 'Smith'); 
INSERT INTO customer_data VALUES (3, 2, 'Mr', 'Jane', 'Green'); 
INSERT INTO customer_data VALUES (4, 2, 'Miss', 'Jane', 'Green'); 
INSERT INTO customer_data VALUES (5, 3, 'Dr', 'Jack', 'Black'); 

结果（查询没有LIMIT和WHERE）：

SELECT CONCAT(title, ' ', forename, ' ', surname) AS name 
FROM  customer c 
JOIN  (
       SELECT MAX(id) max_id, customer_id 
       FROM  customer_data 
       GROUP BY customer_id 
     ) c_max ON (c_max.customer_id = c.customer_id) 
JOIN  customer_data cd ON (cd.id = c_max.max_id); 

+-----------------+ 
| name   | 
+-----------------+ 
| Mr Bob Smith | 
| Miss Jane Green | 
| Dr Jack Black | 
+-----------------+ 
3 rows in set (0.00 sec) 

Answer 2

SELECT CONCAT(title,' ',forename,' ',surname) AS name * FROM customer c 
INNER JOIN customer_data d on c.id=d.customer_id WHERE name LIKE '%Smith%' 

我认为你需要改变 c.customer_id到c.id

其他更新表结构

Answer 3

这是一个很好的想法，记录实际数据为“CUSTOMER_DATA”表。有了这些数据，您可以根据需要从“customer_data”表中选择所有数据。

Answer 4

这可能有助于

How to select the most recent set of dated records from a mysql table

您可以使用子查询来获取最新的结果，然后加入到你的客户。

Answer 5

。假定在customer_data自动增量列被命名为Id，你可以这样做：

SELECT CONCAT(title,' ',forename,' ',surname) AS name * 
FROM customer c 
    INNER JOIN customer_data d 
     ON c.customer_id=d.customer_id 
WHERE name LIKE '%Smith%' 
    AND d.ID = (
       Select Max(D2.Id) 
       From customer_data As D2 
       Where D2.customer_id = D.customer_id 
       ) 
LIMIT 10, 20 

Answer 6

对于任何必须使用旧版本的MySQL（5.0之前版本）您无法对此类查询执行子查询。这是我能够做的解决方案，它似乎工作得很好。

SELECT MAX(d.id), d2.*, CONCAT(title,' ',forename,' ',surname) AS name 
FROM customer AS c 
LEFT JOIN customer_data as d ON c.customer_id=d.customer_id 
LEFT JOIN customer_data as d2 ON d.id=d2.id 
WHERE CONCAT(title, ' ', forename, ' ', surname) LIKE '%Smith%' 
GROUP BY c.customer_id LIMIT 10, 20; 

本质上讲，这是找到你的数据表的最大ID其连接到客户，然后加入数据表中发现的最大的ID。原因是因为选择组的最大值并不能保证其余数据与该id匹配，除非您将其重新加入到自身。

我还没有在较新版本的MySQL上测试过它，但它在4.0.30上有效。

Answer 7

如果您正在处理繁重的查询，最好移动where子句中最新一行的请求。它速度更快，看起来更干净。

SELECT c.*, 
FROM client AS c 
LEFT JOIN client_calling_history AS cch ON cch.client_id = c.client_id 
WHERE 
    cch.cchid = (
     SELECT MAX(cchid) 
     FROM client_calling_history 
     WHERE client_id = c.client_id AND cal_event_id = c.cal_event_id 
    ) 

Answer 8

你也可以做到这一点

SELECT CONCAT(title, ' ', forename, ' ', surname) AS name 
FROM  customer c 
LEFT JOIN (
       SELECT * FROM customer_data ORDER BY id DESC 
     ) customer_data ON (customer_data.customer_id = c.customer_id) 
GROUP BY c.customer_id   
WHERE  CONCAT(title, ' ', forename, ' ', surname) LIKE '%Smith%' 
LIMIT  10, 20;