尝试左连接3个ID可能相同的表，我通过类型定义它

Question

Okay, so I have 3 tables:

users

CREATE TABLE IF NOT EXISTS `users` (
  `user_id` int(11) NOT NULL,
  `user_username` varchar(25) NOT NULL,
  `user_email` varchar(100) NOT NULL,
  `user_password` varchar(255) NOT NULL,
  `user_enabled` int(1) NOT NULL DEFAULT '1',
  `user_staff` varchar(15) NOT NULL DEFAULT '',
  `user_account_type` varchar(20) NOT NULL DEFAULT '0',
  `user_registerdate` date NOT NULL,
  `user_twofactor` int(11) NOT NULL DEFAULT '0',
  `user_twofackey` varchar(255) NOT NULL,
  `user_forgot_email_code` varchar(255) NOT NULL,
  `user_emailverified` varchar(25) NOT NULL DEFAULT 'unverified',
  `user_banned` varchar(25) NOT NULL DEFAULT 'unbanned',
  `user_has_avatar` int(11) NOT NULL DEFAULT '0',
  `user_has_banner` int(11) NOT NULL DEFAULT '0'
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=latin1;

--
-- Dumping data for table `users`
--

INSERT INTO `users` (`user_id`, `user_username`, `user_email`, `user_password`, `user_enabled`, `user_staff`, `user_account_type`, `user_registerdate`, `user_twofactor`, `user_twofackey`, `user_forgot_email_code`, `user_emailverified`, `user_banned`, `user_has_avatar`, `user_has_banner`) VALUES
(1, 'fhfhfhf', 'lol@gmail.com', 'removed', 1, 'admin', 'Business', '2015-07-21', 0, '0', '0', 'unverified', 'unbanned', 1, 0);

company

CREATE TABLE IF NOT EXISTS `company` (
  `company_id` int(11) NOT NULL,
  `company_name` varchar(100) NOT NULL,
  `company_user` int(11) NOT NULL,
  `company_enabled` varchar(50) NOT NULL DEFAULT 'enabled',
  `company_has_avatar` int(5) NOT NULL DEFAULT '0',
  `company_has_banner` int(5) NOT NULL DEFAULT '0'
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;

--
-- Dumping data for table `company`
--

INSERT INTO `company` (`company_id`, `company_name`, `company_user`, `company_enabled`, `company_has_avatar`, `company_has_banner`) VALUES
(1, 'Rad', 3, 'enabled', 0, 0);

training_company

CREATE TABLE IF NOT EXISTS `training_company` (
  `training_company_id` int(11) NOT NULL,
  `training_company_name` varchar(100) NOT NULL,
  `training_company_user` int(11) NOT NULL,
  `training_company_enabled` varchar(50) NOT NULL DEFAULT 'enabled',
  `training_company_has_avatar` int(5) NOT NULL DEFAULT '0',
  `training_company_has_banner` int(5) NOT NULL DEFAULT '0'
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1;

--
-- Dumping data for table `training_company`
--

INSERT INTO `training_company` (`training_company_id`, `training_company_name`, `training_company_user`, `training_company_enabled`, `training_company_has_avatar`, `training_company_has_banner`) VALUES
(1, '123', 3, 'enabled', 0, 0),
(2, '123', 3, 'enabled', 0, 0),
(3, '123', 3, 'enabled', 0, 0);

Each have a profile, that have an incrementing id, so will have the same id, Iam just defining they via type, so user would be user, training would be training and company would be company, I am allowing a user to follow either one.

SQL

SELECT * FROM timeline_status
LEFT JOIN users
  ON timeline_status.timeline_status_user = users.user_id
LEFT JOIN timeline_likes
  ON timeline_status.timeline_status_id = timeline_likes.timeline_likes_main_status
LEFT JOIN friends
  ON timeline_status.timeline_status_user = friends.friends_friend
LEFT JOIN user_personal_information
  ON timeline_status.timeline_status_user = user_personal_information.user_personal_information_user
LEFT JOIN following
  ON timeline_status.timeline_status_user = following.following
WHERE timeline_status_enabled = 'enabled'
AND timeline_status.timeline_status_type = 'user'
AND (timeline_status.timeline_status_user = :status_user
OR friends.friends_user = :friend_user)
AND (timeline_status_privacy = 'onlyme'
AND timeline_status_user = :status_user2
OR timeline_status_privacy = 'public'
OR timeline_status_privacy = 'private')
GROUP BY timeline_status_id
ORDER BY timeline_status_date DESC
LIMIT :start, :end

So I'd want to select from users if type = user, and row exists in followers and/or friends, select from companies or training from followers if type = company or training.

My status have the company/user/training id, and the type, so I know which table to select the 'user from'

my following table;

CREATE TABLE IF NOT EXISTS `following` (
  `following_id` int(11) NOT NULL,
  `following_user` int(11) NOT NULL,
  `following_type` varchar(50) NOT NULL,
  `following` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=latin1;

--
-- Dumping data for table `following`
--

INSERT INTO `following` (`following_id`, `following_user`, `following_type`, `following`) VALUES
(5, 3, 'company', 14),
(8, 3, 'training', 1);

timeline status:

CREATE TABLE IF NOT EXISTS `timeline_status` (
  `timeline_status_id` int(11) NOT NULL,
  `timeline_status_user` int(11) NOT NULL,
  `timeline_status_privacy` varchar(25) NOT NULL DEFAULT 'public',
  `timeline_status_type` varchar(25) NOT NULL DEFAULT 'user',
  `timeline_status_post` text NOT NULL,
  `timeline_status_date` datetime NOT NULL,
  `timeline_status_enabled` varchar(25) NOT NULL DEFAULT 'enabled'
) ENGINE=InnoDB AUTO_INCREMENT=123 DEFAULT CHARSET=latin1;

--
-- Dumping data for table `timeline_status`
--

INSERT INTO `timeline_status` (`timeline_status_id`, `timeline_status_user`, `timeline_status_privacy`, `timeline_status_type`, `timeline_status_post`, `timeline_status_date`, `timeline_status_enabled`) VALUES
(98, 3, 'private', 'user', 'hello', '2015-10-02 16:29:48', 'enabled'),
(99, 3, 'onlyme', 'user', 'yo', '2015-10-02 16:29:56', 'enabled'),
(100, 3, 'public', 'user', 'fghyjt', '2015-10-02 17:51:28', 'enabled'),
(101, 1, 'private', 'training', 'teest..', '2015-10-03 14:26:45', 'enabled'),
(102, 15, 'public', 'company', 'hello', '2015-10-06 13:32:30', 'enabled');

So how can I do it so if the following type = company select from company, if following tye = training select from training, and if following type = user, keep the sql how it is at the moment. Because at the moment, I am following a company with the id of 1, but there's a user with an id of 1 too, so I am getting their statuses.

Answer 1

Your best bet would be to use the UNION operator to mix them all in 1 table, and then query based on type. For instance, you could do something like this :

SELECT f.*, 
    t.training_company_name as name, 
    null as staff,
    t.training_company_enabled as enabled, 
    t.training_company_has_banner as banner, 
    t.training_company_has avatar as avatar 
FROM following f
INNER JOIN training_company t on f.following_user = t.training_company_user AND f.following_type='training'
UNION ALL
SELECT f.*, 
    c.company_name as name, 
    null as staff,
    c.company_enabled as enabled, 
    c.company_has_banner as banner, 
    c.company_has avatar as avatar 
FROM following f
INNER JOIN company c on f.following_user = c.company_user AND c.following_type='company'
UNION ALL
SELECT f.*, 
    u.user_username as name, 
    u.user_staff as staff, 
    u.user_enabled as enabled, 
    u.user_has_banner as banner, 
    u.user_has avatar as avatar 
FROM following f
INNER JOIN users u on f.following_user = c.company_user AND f.following_type='user'

And from there you will have a derived table/view that will look like

V_followers(timeline_status_id, timeline_status_user, timeline_status_privacy, timeline_status_type, timeline_status_post, timeline_status_date, timeline_status_enabled, name, staff, enabled, banner, avatar) .

I'm not 100% certain the syntax is MySql-correct though, but the idea remains the same.

Answer 2

I think you will need another variable to tell you the type in addition to the user id. Then you can wrap both up in a CASE statement, like so:

WHERE 
CASE WHEN type = 'USER' THEN timeline_status.timeline_status_user = id
WHEN type = 'FRIENDS' THEN friends.friends_user = id
WHEN type = 'FOLLOWING' THEN following.user = id
END

Answer 3

In your question you actually ask few questions)

1) And company and training_company have user, that's why you can join this tables, left join will takes only needed rows and from appropriate tables, and with case you can select needed field:

select
    u.user_id, u.user_account_type,
    case when u.user_account_type = 'Business' then c.company_name
        else tc.training_company_name
        end as name_of_company
from users u
left join company as c on u.user_id = c.company_user
left join training_company as tc on u.user_id = tc.training_company_user
;

2) Table following contains and users and companies that's why you can do the same:

select
    f.following_user,
    f.following_type,
    case
        when f.following_type = 'company' then c.company_name
        when f.following_type = 'training' then tc.training_company_name
        else u.user_username
    end as name
from following f
left join users u on f.following_user = u.user_id
-- here you can add inner joins to followers, friends etc
left join company as c on f.following_user = c.company_user
left join training_company as tc on f.following_user = tc.training_company_user
;

3) I think your schema pretty simple and i'm sure that you can use joins to achieve your desires. I would like emphasize one moment if you have choice: user or company etc - use left join, if you have restrictions users with followers or friends etc - use inner join... (it should work faster)...

Hope i correctly understood you, and this info will help you!

Answer 4

It seems like you have a situation whereby you have the concept of an entity that can post statuses, and has other information relevant to that.

These entities come in three forms; user, company, training_company. Each of these forms may have more specific sub details.

Have you considered placing all the entity info in one table:

• entity - id, type, name, enabled, banner, avatar

Then implementing a has_one relationship to any information relevant to the sub_type:

• user - entity_id, ... user specific fields
• company - entity_id, .. company specific fields
• training_company - entity_id .. training company specific fields

Usually you will be doing one of the following:

• aggregate stats regarding entities/statuses - select from entity

• lists of statuses - select from entity

• aggregate stats regarding one specific type - select from type_table join entity

• list inc. detail of one specific type - select from type_table join entity

• details of one entity - select from type_table join entity

In the rare case of needing to display full details of a list of entities you can either use a UNION query or just run one query for the entities and then 3 queries on the sub_types WHERE entity_id IN (pulled entity ids).. this data is often paginated anyway, so the performance should be good enough.

We have used this structure in our projects to good effect, be aware it will require more complicated CRUD operations.