Posted by Ciaran on 07/22/07 11:04

On Jul 15, 12:54 am, "nelson.salva...@gmail.com"
<nelson.salva...@gmail.com> wrote:
> My Example:
> Field: Bank Account Nº: 12353545456
> Field: Bank Account Nº:
>
> The nº must be unique but could be empty also...

If you introduce a UNIQUE constraint on a VARCHAR field, there can
only be one row that has the empty string ("") as its value.

However, if you allow the column to be NULL, you can insert as many
NULL records as you like.

-Ciaran McNulty

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