Posted by Jochem Maas on 10/11/05 10:44

Richard Lynch wrote:
> On Mon, October 10, 2005 3:24 pm, Dan McCullough wrote:
>
>>create a function to check if the rndnumber=couponcode row count = 0
>>if not then redo rndnumber if it does = 0 then insert rndnumber
>
>
> Noooooooooooooooooooooooooooo!
>
> You are creating a RACE CONDITION in which ONE user might generate a
> 'valid' code, and ANOTHER user might generate a 'valid' code AT THE
> SAME TIME, and then they BOTH get the same coupon code.
>
> The probability of this is very very very low, but still NOT zero.
>
> And it's the kind of thing that won't show up in testing, but sure as
> God made little green apples, it WILL happen at the worst possible
> time after you "go live"

lol. Richard you should write a book :-) (or should that be 'another book'?)

>
> The database engine has a *TON* of code in it to avoid this kind of
> Bad Thing happening.
>
> Use it.
>
> create a UNIQUE INDEX on the column that needs to be unique.
>
> Trap the INSERT error.
>

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