Declare variable MySQL trigger and create table using that variable - mysql

Question

I have a event in which I am storing a string in a variable. Now I want to use that variable to create a new table. Everytime my event runs it creates table with the name of "mon". What is I am doing wrong ?
BEGIN
DECLARE onlyweek INT;
DECLARE mon VARCHAR(20);
SET #mon = "rehan";
CREATE TABLE mon(
id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
capacity INT NOT NULL
);
END

Answer 1

Because you use mon instead of #mon. And even then it wont work because you need dynamic SQL for that.
But what is even more important:
Don't do that!
Don't create a table on the fly. Table designs should be static. That smells like a big design flaw.

Answer 2

This is a design mistake. For example, you need to make report for the year. In your design you have to join 12 tables and where-s how to join. And this is very slow.
Better design is creating 2 tables - "months" and "reporting_periods" with foreign key to table 'months'. This way when you need year report - you join only 2 tables by ID with "where".
Table 'months' can be filled once a year using same mysql events.
Then use mysql "stored procedure" (and mysql event) for periodic insert into reporting_period with month id. Months` names can include year as "bad way" or have the field 'year' = 'better one'.
CREATE TABLE months(
id int auto_increment,
name varchar(10),
number int not null,
year int not null,
constraint monthes_pk
primary key (id)
);
and reporting_period
CREATE TABLE reporting_period(
id INT auto_increment,
period_id INT NOT NOT,
capacity INT NOT NULL,
constraint `reporting_period_pk`
primary key (id),
constraint `reporting_period__fk`
foreign key (period_id) references months (id)
);
More about DB design: normalization