Nulls

All data types include the null value. Distinct from all nonnull values, the null value is a special value that denotes the absence of a (nonnull) value.

Although all data types include the null value, some sources of values cannot provide the null value. For example, constants, columns that are defined as NOT NULL, and special registers cannot contain null values; the COUNT and COUNT_BIG functions cannot return a null value; and ROWID columns cannot store a null value although a null value can be returned for a ROWID column as the result of a query.