Auto_increment trigger - mysql

Question

I need to auto_increment the primary key in a mysql database using a trigger. Unfortunately, I am not quite sure how to do this. In the sample code I have provided, I need the employee table primary key to auto_increment beginning with an empty table and a starting value of 200. Then, I need each new insert to increment by 1.Thanks for looking and I hope you are able to help me.
CREATE TABLE department (
dept_name VARCHAR(50) NOT NULL Primary Key
);
CREATE TABLE employee (
emp_id INT(6) unsigned Default 0 Not NULL
, last_name VARCHAR(25) NOT NULL
, first_name VARCHAR(40) NOT NULL
, dept_name VARCHAR(50) NOT NULL
, PRIMARY KEY(emp_id, dept_name)
, FOREIGN KEY(dept_name) REFERENCES department (dept_name)
);

Answer 1

There are several things you need to do:
Declare the emp_id column as AUTO_INCREMENT;
Set the value of AUTO_INCREMENT property of the table to 200;
Do not provide any value for column emp_id when you INSERT rows in table employee.
Change the table creation as below:
CREATE TABLE employee (
emp_id INT(6) UNSIGNED NOT NULL AUTO_INCREMENT,
last_name VARCHAR(25) NOT NULL,
first_name VARCHAR(40) NOT NULL,
dept_name varchar(50) NOT NULL
PRIMARY KEY(emp_id),
FOREIGN KEY(dept_name) REFERENCES department_tbl(dept_name)
) AUTO_INCREMENT=200;
If the table has an AUTO_INCREMENT column then it must be the PRIMARY KEY of the table. I removed dept_name from the definition of the PK above. I also removed the default value 0 from the emp_id column. It's default value is generated by MySQL using the AUTO_INCREMENT policy.
When you INSERT a new record into the employee table all you have to do is to not provide any value for the emp_id column:
INSERT INTO employee (last_name, first_name, dept_name)
VALUES ('Doe', 'John', 'accounting');
Then use the LAST_INSERT_ID() MySQL function to retrieve the value of the emp_id generated on insertion.
The language or the library you use to develop the client application probably has a function that wraps LAST_INSERT_ID() and returns its value.