Unique fields on mySQL table - generating promo codes - mysql

Question

I am developing a PHP script and I have a table like this:
TABLE_CODE
code varchar 8
name varchar 30
this code column has to be a code using random letters from A to Z and characters from 0 to 9 and has to be unique. all uppercase. Something like
A4RTX33Z
I have create a method to generate this code using PHP. But this is a intensive task because I have to query the database to see if the generated code is unique before proceeding and the table may have a lot of records.
Because I know mySQL is a bag of tricks but not having advanced knowledge about it now, I wonder if there's some mechanism that could be built in a table to run a script (or something) every time a new record in created on that table to fill the code column with a unique value.
thanks
edit: What I wonder is if there's a way to created the code on-the-fly, as the record is being added to the table and that code being unique.

Answer 1

Better generate these codes in SQL. This is 8-character random "Promo code generator":
INSERT IGNORE INTO
TABLE_CODE(name, code)
VALUES(
UPPER(SUBSTRING(MD5(RAND()) FROM 1 FOR 8)), -- random 8 characters fixed length
'your code name'
)
Add UNIQUE on code field as #JW suggested, and some error-handling in PHP, because sometimes generated value may be not UNIQUE, and MySQL will raise error in that situation.

Answer 2

Adding a UNIQUE constraint on the code column is the first thing you would need to do. Then, to insert the code I would write a small loop like this:
// INSERT IGNORE will not generate an error if the code already exists
// rather, the affected rows will be 0.
$stmt = $db->prepare('INSERT IGNORE INTO table_code (code, name) VALUES (?, ?)');
$name = 'whatever name';
do {
$code = func_to_generate_code();
$stmt->execute(array($code, $name));
} while (!$stmt->rowCount()); // repeat until at least one row affected
As the table grows the number of loops may increase, so if you feel it should only try three times, you could add it as a loop condition and throw an error if that happens.
Btw, I would suggest using transactions to make sure if an error occurs after the code generation, rolling back will make sure the code is removed (can be reused).