>can you safely use a key here ?
>
>I am concerned that the table may change over the years, and keys get re-used!


I don't worry about it. With integers you can get 4 billion unique values if you use negative numbers. The storage space is minimal too, only 4 bytes.

>
>The keys may have to control both current and archival data, but the system may not have the archive data available all the time! ( either a value may get two keys, or one key may refer to two values , unless you keep a table with all keys that have been created and their value, a serious problem if you get audited 5 years down the road! )

Yes, you keep track of the last used number. That means one table that handles this for you.

>
>
>I suspect that there is no ultimately no safe way to control a big field with a small one!
>
>However, if you use a simple hex look up system, you get far more mileage from your 6 byte field!
>( create a look up table that stores all used strings to a new hex value, , thus using all 255 values instead of just the commonly used 10 numeric + 26 or 52 alpha, thus the field can hold about 30,000,000,000,000 ( 256 ^ 6) values, which should be enough! )

You could use a hex system. There are lots of options other than mine. However, many people have told me they use my code and have never had a problem. Neither have I.

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>The math isn't confirmed, but I hope you get the ideas & concerns
>
>Mike