MySQL僅加入最近一行？

Question

我有一個表顧客存儲customer_id，電子郵件和參考。還有一個額外的表customer_data，用於存儲對客戶進行的更改的歷史記錄，即插入新行時發生更改。

爲了在表中顯示客戶信息，需要連接兩個表，但只有customer_data中最近的一行應該連接到customer表。

由於查詢是分頁的，所以有一個限制和一個偏移量。

我該怎麼用MySQL做到這一點？我想我希望把不同之處在那裏的某個地方......

在一分鐘的查詢就像是這個 -

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，我是正確的思維，我可以在使用CONCAT與LIKE這條路？

（我明白，INNER JOIN可能是錯誤的連接類型使用的。其實，我不知道有什麼區別之間的不同連接。我要去看看現在！）

Answer 1

你可能想嘗試以下操作：

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，一個JOIN僅僅是INNER JOIN的代名詞。

測試用例：

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'); 

結果（查詢沒有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%' 

我認爲你需要改變 c.customer_id到c.id

其他更新表結構

Answer 3

這是一個很好的想法，記錄實際數據爲「CUSTOMER_DATA」表。有了這些數據，您可以根據需要從「customer_data」表中選擇所有數據。

Answer 4

這可能有助於

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

您可以使用子查詢來獲取最新的結果，然後加入到你的客戶。

Answer 5

。假定在customer_data自動增量列被命名爲Id，你可以這樣做：

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

對於任何必須使用舊版本的MySQL（5.0之前版本）您無法對此類查詢執行子查詢。這是我能夠做的解決方案，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; 

本質上講，這是找到你的數據表的最大ID其連接到客戶，然後加入數據表中發現的最大的ID。原因是因爲選擇組的最大值並不能保證其餘數據與該id匹配，除非您將其重新加入到自身。

我還沒有在較新版本的MySQL上測試過它，但它在4.0.30上有效。

Answer 7

如果您正在處理繁重的查詢，最好移動where子句中最新一行的請求。它速度更快，看起來更乾淨。

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

你也可以做到這一點

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;