In Defense of Nulls

Nulls in Relational Database

Nulls represent real world situations - that of missing information. The situation arises in filling out forms for example. When individuals are unable or unwilling to enter a requested piece of information, they resort to various devices - leaving the entry blank (this may also indicate they didn't even examine the question), entering N/A for Not Applicable, drawing a horizontal line through the space, etc.. In pre-relational systems, the non-entry of information is often represented by a blank value or for numeric fields - 0 or -1. In a relational system, nulls are used.

Some important uses for nulls in relational databases are:

Finally, nulls have counterparts in other programming paradigms. Functional programming systems have the concept of undefined or ground, represented by _|_. 3-valued logic is used with _|_.

3-Valued Logic (3VL) is discussed in the next section.

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