Re: Generating unique values for TEXT columns

SELECT max, then treat the string as a sequence of characters and
increment the last character, rippling the carry if there is one :

carry = 1
l = len(s)-1
while carry and l>=0:
c = s[l]
c += carry
if c>max_allowed_char:
c = min_allowed_char
carry = 1
else:
carry = 0
s[l] = c

if carry:
s = min_allowed_char + s

If two transactions do the same at the same time, you're out of luck
though !

*** Better solution :

if the value was human-entered, prefix it with 'H',
if it's auto generated, use 'A' concatenated with the value from a sequence

thus the user-entered values can't clahs with the sequence values ; the
sequence values are by definition unique ; and all is well.

or something like that...

On Mon, 3 Jan 2005 11:53:44 -0500, Frank D. Engel, Jr.
<fde101(at)fjrhome(dot)net> wrote:

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> Is there any "convenient" way to generate (on request) a unique value
> for a TEXT column? I have a situation in which I want users of my
> front-end program to be able to manually enter values for this column,
> but if they leave it blank (in the front-end), to have the database
> automatically fill in a unique value. I would like to restrict the
> unique values to (for example) digits and uppercase letters (this is
> flexible, but the uniqueness of the values should be visually
> discernible, and all characters should be printable).
>
> I know how to do this with a numeric column (I can just SELECT MAX on
> the column and add one, for example), but how can this be done with a
> TEXT column?
>
> Thank you!
>
> - -----------------------------------------------------------
> Frank D. Engel, Jr. <fde101(at)fjrhome(dot)net>
>
> $ ln -s /usr/share/kjvbible /usr/manual
> $ true | cat /usr/manual | grep "John 3:16"
> John 3:16 For God so loved the world, that he gave his only begotten
> Son, that whosoever believeth in him should not perish, but have
> everlasting life.
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> iD8DBQFB2XiY7aqtWrR9cZoRAqATAJ46xJ3bwsZVpIda0iMSSdcm3/8YKACePSC3
> 2JAngWmFOlkzC5fNE6HKYMU=
> =pblY
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>
>
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