Alphanumeric field in MySQL

Question

I need to create a character field with some rules, they are,

Field name:

1. contract_number.

Rules: Contract Number

1. Contract number must be alphanumeric.
2. Contract number must be unique.
3. Contract number must be auto increment.

Example:

CBE27032014001

Here, the contract number represents the following terms,

CBE 27 03 2014 001

1. CBE - (Coimbatore) City Name.
2. 27032014 - Date Month Year.
3. 001 - Contract reference number (just numeric value).

My database contract table as follows,

create table contract
(
contract_id int not null auto_increment,
contract_number  char(14) not null,
................
unique key(contract_number),
primary key(contract_id)
);

This is completely new to me,

1. How to implement this task?
2. Is there any general logic to implement such kind of tasks?
3. Any suggestions to split the big task into smaller tasks, so that it will easy to understand?

Thanks.