MySQL是否只加入最近一行?

您可以尝试以下操作:

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;

JOIN 只是 INNER JOIN .

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(不带 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)

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
   )

假定中的自动增量列 customer_data 被命名为 Id ,您可以执行以下操作:

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

对于任何必须使用较旧版本MySQL(5.0之前的版本)的用户,您不能对这种类型的查询执行子查询。这是我能做的解决方案,看起来效果很好。

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,这是查找数据表的max id,将其连接到客户,然后将数据表连接到找到的max id。这是因为选择组的最大值并不能保证其余数据与id匹配,除非您将其重新连接到自身。

我还没有在MySQL的新版本上测试过这个,但是它可以在4.0.30上运行。

我知道这个问题由来已久,但多年来一直备受关注,我认为它缺少了一个可能对类似案件中的人有所帮助的概念。我把它加在这里是为了完整。

如果你 可以 ,但是,如果要修改您的模式,我建议您在 customer id 最新的 customer_data 此客户的记录:

CREATE TABLE customer (
  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  current_data_id INT UNSIGNED NULL DEFAULT NULL
);

CREATE TABLE customer_data (
   id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
   customer_id INT UNSIGNED NOT NULL, 
   title VARCHAR(10) NOT NULL,
   forename VARCHAR(10) NOT NULL,
   surname VARCHAR(10) NOT NULL
);

查询客户

SELECT c.*, d.title, d.forename, d.surname
FROM customer c
INNER JOIN customer_data d on d.id = c.current_data_id
WHERE ...;

缺点是在创建或更新客户时会有额外的复杂性。

更新客户

表,并更新 顾客 记录。

INSERT INTO customer_data (customer_id, title, forename, surname) VALUES(2, 'Mr', 'John', 'Smith');
UPDATE customer SET current_data_id = LAST_INSERT_ID() WHERE id = 2;

创建客户

创建客户只是插入 顾客 输入,然后运行相同的语句:

INSERT INTO customer () VALUES ();

SET @customer_id = LAST_INSERT_ID();
INSERT INTO customer_data (customer_id, title, forename, surname) VALUES(@customer_id, 'Mr', 'John', 'Smith');
UPDATE customer SET current_data_id = LAST_INSERT_ID() WHERE id = @customer_id;

创建/更新客户的额外复杂性可能令人恐惧,但可以通过触发器轻松实现自动化。

Customer 模型看起来像:

class Customer
{
    private int id;
    private CustomerData currentData;

    public Customer(String title, String forename, String surname)
    {
        this.update(title, forename, surname);
    }

    public void update(String title, String forename, String surname)
    {
        this.currentData = new CustomerData(this, title, forename, surname);
    }

    public String getTitle()
    {
        return this.currentData.getTitle();
    }

    public String getForename()
    {
        return this.currentData.getForename();
    }

    public String getSurname()
    {
        return this.currentData.getSurname();
    }
}

你的永恒 CustomerData 仅包含getter的模型:

class CustomerData
{
    private int id;
    private Customer customer;
    private String title;
    private String forename;
    private String surname;

    public CustomerData(Customer customer, String title, String forename, String surname)
    {
        this.customer = customer;
        this.title    = title;
        this.forename = forename;
        this.surname  = surname;
    }

    public String getTitle()
    {
        return this.title;
    }

    public String getForename()
    {
        return this.forename;
    }

    public String getSurname()
    {
        return this.surname;
    }
}

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%' 

c、 客户id到c.id

else更新表结构

你也可以这样做

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;

将实际数据记录到 客户数据