在MySQL的一个表中存储100多个列的最佳方法

Question

I am working on a data model where I need to store Employee's basic details and his rating of skillsets in MySQL database.

The number of skillsets for each employee is more than 100. So the information I need to store is as following: Employee ID, Name , Department , Contact info, Skillset1,Skillset2,Skillset3, ... , Skillset115

Is creating one table with approximately 120 columns is good approach? If not, what is the best practice to deal with this kind of requirement.

Answer 1

No. You should have a separate table with one row per employee and per skill:

create table employeeSkills (
    employeeSkillId int auto_increment primary key,
    employeeId int not null,
    skill varchar(255),
    constraint fk_employeeSkills_employeeid foreign key (employeeId) references employees(employeeId)
);

In fact, you should really have two extra tables. The skills themselves should be stored in a separate table and the above should really be:

create table employeeSkills (
    employeeSkillId int auto_increment primary key,
    employeeId int not null,
    skillId int,
    constraint fk_employeeSkills_employeeid foreign key (employeeId) references employees(employeeId),
    constraint fk_employeeSkills_skillid foreign key (skillId) references skills(skillId)
);

This type of table is called a "junction table", and is common in any properly constructed data model.

Answer 2

You need to create two tables that would handle the skills and the assigned skill for each employee.

This would give you a proper order in your database and also will extend your options in the future. It'll be better in search, add and assign skills to each employee. It's even more organized and would be able to be expanded easily such as adding skills category and sub-category.

The two tables schema should be something like this :

CREATE TABLE Skills (
    Skill_ID            INT NOT NULL AUTO_INCREMENT, 
    Skill_Description   VARCHAR(250), 
    PRIMARY KEY (`Skill_ID`)
); 

CREATE TABLE EmpolyeeSkills (
    ES_ID       INT NOT NULL AUTO_INCREMENT,
    Skill_ID    INT, 
    Employee_ID INT,
    PRIMARY KEY (`ES_ID`),
    CONSTRAINT FK_EMPLOYEEID FOREIGN KEY (Employee_ID) REFERENCES Employees(Employee_ID),
    CONSTRAINT FK_SKILLID FOREIGN KEY (Skill_ID) REFERENCES Skills(Skill_ID)
); 

The Skills table will assign an ID for each skill, and it'll be in a separate table. This will make you have a unique skills list, there won't be any redundancy. Then, you'll use EmployeeSkills to save the assigned skills on each Employee_ID. Which you can use it later on to join it with other records.

The FOREIGN KEY on Employee_ID and Skill_ID will help you in monitoring the skills between them. The ES_ID primary key for EmpolyeeSkills will be an additional advantage that can be helpful in the future. For instance, if you want to know the latest skill that has been assigned, then your faster approach will be getting the last ES_ID as it's an AUTO_INCREMENT. This is just one advantage from tons of others.