-1

我对我的 mysql 数据库有以下查询。

SELECT
  mn.id,
  mn.created_date,
  mn.created_by,
  mnt.description,
  u.handle,
  mn.admin_request_company_id
FROM member_notification mn,
  member_notification_type mnt,
  member m,
  user u
WHERE mn.member_notification_type_id = mnt.id
    AND mnt.name = 'COMPANYVALIDATION'
    AND mn.created_by = m.id
    AND m.user_id = u.id;

这工作正常，但是我现在需要扩展它以从另一个表中获取公司名称。问题是，要做到这一点，我需要使用键 mn.admin_request_company_id 重新加入成员表，但是我不知道该怎么做。

我尝试创建一个成员 m2 表，但出现错误。我想要实现的是类似于以下伪代码的内容：

SELECT
  mn.id,
  mn.created_date,
  mn.created_by,
  mnt.description,
  u.handle,
  mn.admin_request_company_id,
  /*c.company_name*/
FROM member_notification mn,
  member_notification_type mnt,
  member m,
  /*member m2,*/
  /*company c,*/
  /*user u*/
WHERE mn.member_notification_type_id = mnt.id
    AND mnt.name = 'COMPANYVALIDATION'
    AND mn.created_by = m.id
    AND m.user_id = u.id
   /* AND mn.admin_request_company_id = m2.company_id
    AND m2.company_id = c.id*/

编辑 表结构如下：

CREATE TABLE member_notification (
id INT NOT NULL AUTO_INCREMENT,
item_id INT NULL,
member_id INT NULL,
text VARCHAR(1) NOT NULL,
member_notification_type_id INT NULL,
marked_read VARCHAR(1) NOT NULL,
created_date DATETIME NOT NULL,
created_by VARCHAR(50) NOT NULL,
admin_request_company_id INT NULL,
PRIMARY KEY (id)
) ENGINE=innodb;

CREATE TABLE member_notification_type (
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(20) NOT NULL,
description VARCHAR(50) NULL,
PRIMARY KEY (id)
) ENGINE=innodb;

CREATE TABLE member (
id INT NOT NULL AUTO_INCREMENT,
user_id INT NULL,
company_id INT NULL,
soft_delete VARCHAR(10) DEFAULT 'N',
member_status_id INT NOT NULL,
PRIMARY KEY (id)
) ENGINE=innodb;


CREATE TABLE user (
id INT NOT NULL AUTO_INCREMENT,
handle VARCHAR(50) NOT NULL,
first_name VARCHAR(50) NOT NULL,
last_name VARCHAR(50) NOT NULL,
date_of_birth VARCHAR(50) NULL,
soft_delete VARCHAR(10) DEFAULT 'N',
PRIMARY KEY (id)
) ENGINE=innodb;

CREATE TABLE company (
id INT NOT NULL AUTO_INCREMENT,
owning_company_id INT NULL,
company_type_id INT NULL,
name VARCHAR(50) NOT NULL,
company_details_id INT NULL,
PRIMARY KEY (id)
) ENGINE=innodb;
4

3 回答 3

2

似乎您只想使用以下内容，它只是向member表添加了第二个连接：

SELECT
  mn.id,
  mn.created_date,
  mn.created_by,
  mnt.description,
  u.handle,
  mn.admin_request_company_id,
  c.name
FROM member_notification mn
INNER JOIN member_notification_type mnt
  on mn.member_notification_type_id = mnt.id
INNER JOIN member m1
  on mn.created_by = m1.id
INNER JOIN user u
  on m1.user_id = u.id
INNER JOIN member m2
  on mn.admin_request_company_id = m2.company_id
INNER JOIN company c
  on m2.company_id = c.id
WHERE mnt.name = 'COMPANYVALIDATION'

请注意，我将您当前在WHERE子句中的联接更改为 ANSI 联接语法。我还在INNER JOIN表格之间使用了一个，您可能需要使用一个LEFT JOIN.

于 2013-01-22T11:04:47.720 回答
1

要在一个表上连接两次，请使用不同的名称选择该表两次：

SELECT
  ...
FROM 
  member m1,
  member m2,
  someCouplingTable t
WHERE
  m1.Id = t.leftId
  AND m2.Id = t.rightId
于 2013-01-22T11:00:36.457 回答
1

这是你如何做到的

SELECT
  mn.id,
  mn.created_date,
  mn.created_by,
  mnt.description,
  u.handle,
  mn.admin_request_company_id
FROM member_notification mn
  left join member_notification_type mnt
    on mnt.id = mn.member_notification_type_id
  left join member m
    on m.id = mn.created_by
  left join user u
    on u.id = m.user_id
  left join company as c
    on c.id = m.company_id
where mnt.name = 'COMPANYVALIDATION'
于 2013-01-22T11:08:25.767 回答