Consider the tautology: an unnecessary construct that adds no meaning, context, or understanding and may as not exist. In linguistics, it can come in the form of superfluous modifiers such as adequate enough and true fact. In procedural code, it’s simply wrapping code in an “if (true) {…}” block. But in a database table, representing the tautology can be especially tricky.

Fortunately, John’s has solved this problem by inventing a new SQL data type that can be used when a BIT column would allow too much variation in the data. Simply add a BIT column to your table along with a CHECK constraint enforcing that column to be zero.

CREATE TABLE [CustomerOrder] (


    ... snip ...
    [IsFulfilled] BIT NOT NULL
       CONSTRAINT [CK_CustomerOrder_IsFulfilled]
       CHECK  ( [IsFulfilled] = 0 )


Just think of the possibilities! With the tautology type, you can add columns like [DoesThisRowExist] and [IsValidOrInvalid], thereby effectively encoding zero bits of information.

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