The NULL predicate combined with NOT manipulates rows that do not contain any null values in their table columns.

When NOT is not combined with the NULL predicate, the rows containing the null value become the target of manipulation.

The following figure shows, as an example of a data search using the NULL predicate with NOT specified, the procedure for searching the order table for the form numbers, product codes, and quantities ordered for all customer codes that have been set (non-null values).

Figure 2-27 Data search example using a NULL predicate with NOT