Re: Re: Mapping output from a SEQUENCE into something non-repeating/colliding but random-looking?

On May 3, 2009, at 9:00 AM, Craig Ringer wrote:

> CREATE OR REPLACE FUNCTION luhn_verify(int8) RETURNS boolean AS $$
> SELECT
> -- Add the digits, doubling odd-numbered digits (counting left with
> -- least significant as zero), and see if the sum is evenly
> -- divisible by zero.

I think you mean divisible by 10 here, numbers are generally not
divisible by zero ;)

Regardless, thanks for posting these functions, I'm sure they'll come
in handy some time.

>
> MOD(SUM(
> -- Extract digit `n' counting left from least significant as
> zero
> MOD( ( $1::int8 / (10^n)::int8 ), 10::int8)
> -- Double odd-numbered digits
> * (MOD(n,2) + 1)
> ), 10) = 0
> FROM generate_series(0, ceil(log( $1 ))::integer - 1) AS n;
> $$ LANGUAGE 'SQL'
> IMMUTABLE
> STRICT;
>
> COMMENT ON FUNCTION luhn_verify(int8) IS 'Return true iff the last
> digit
> of the input is a correct check digit for the rest of the input
> according to Luhn''s algorithm.'

Alban Hertroys

--
If you can't see the forest for the trees,
cut the trees and you'll see there is no forest.

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