MySQL的速度：具有多个列的表或使用联接的2个表

Question

I tried searching for this but I could not find anything about this but design choices.

So my question is like the title. What is faster? Create 1 table with many columns or create 2 or 3 (for many to many) tables with join(s).

I like the idea of have multiple tables so the data is separated. Mostly for many to many like data. But my friend told me having 5 columns with boolean is just fine. But I like the idea of have a table with the settings and then a table between with user.id and setting.id. But my question is also, does it have a impact on the query?

example:

Users
- id
- Email
- SettingA
- SettingB
- SettingC

OR example:

Uers
- id
- email
Users_Settings
- user_id
- setting_id
Settings
- id
- someSettingsValue

What woult be faster for Mysql to query the data? (retrieving settings for user)

Answer 1

与单个表字段相比，仅2 r 3之间的连接将花费时间。

Answer 2

It's not about preferring single table with many columns or preferring multiple tables. It's about Normalization.

According to your provided schema, if all users will always have three settings, ie Setting A, B and C, then it's better to create single table with these three columns for settings.

users table:
    +----------+--------------+------+-----+---------+----------------+
    | Field    | Type         | Null | Key | Default | Extra          |
    +----------+--------------+------+-----+---------+----------------+
    | id       | int(11)      | NO   | PRI | NULL    | auto_increment |
    | Email    | varchar(128) | NO   |     | NULL    |                |
    | SettingA | tinyint(1)   | NO   |     | NULL    |                |
    | SettingB | tinyint(1)   | NO   |     | NULL    |                |
    | SettingC | tinyint(1)   | NO   |     | NULL    |                |
    +----------+--------------+------+-----+---------+----------------+

But if any of the setting is saved is null, then better is to create separate table for settings and then a pivot table for maintaining users' settings without primary key.

users table:
    +-------+--------------+------+-----+---------+----------------+
    | Field | Type         | Null | Key | Default | Extra          |
    +-------+--------------+------+-----+---------+----------------+
    | id    | int(11)      | NO   | PRI | NULL    | auto_increment |
    | Email | varchar(128) | NO   |     | NULL    |                |
    +-------+--------------+------+-----+---------+----------------+

settings table:
    +---------------+------------+------+-----+---------+----------------+
    | Field         | Type       | Null | Key | Default | Extra          |
    +---------------+------------+------+-----+---------+----------------+
    | id            | int(11)    | NO   | PRI | NULL    | auto_increment |
    | setting_value | tinyint(1) | NO   |     | NULL    |                |
    +---------------+------------+------+-----+---------+----------------+

setting_user pivot table:
    +------------+---------+------+-----+---------+-------+
    | Field      | Type    | Null | Key | Default | Extra |
    +------------+---------+------+-----+---------+-------+
    | setting_id | int(11) | NO   |     | NULL    |       |
    | user_id    | int(11) | NO   |     | NULL    |       |
    +------------+---------+------+-----+---------+-------+

Where setting_user is the pivot table.

One more thing is considered when creating schema, that, will there be always three settings, or will there be more in future, when application is expanded!