Question

I have the following query against my mysql database.

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;

This is working fine however I now need to extend this to go get a company name off another table. The problem is that to do that I need to re-join against the member table using the key
mn.admin_request_company_id, however I’m not sure how to go about this.

I’ve tried creating a member m2 table but I’m getting errors. What I’m trying to achieve is something along the lines of the following pseudo code:

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*/

edit
Table structures as are follows:

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;

Answer 1

It seems like you just want to use the following which just adds a second join to the member table:

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'

Notice, I changed your current joins in the WHERE clause to ANSI join syntax. I also used an INNER JOIN between the tables, you might need to use a LEFT JOIN.