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NOT NULL Column Constraint Constraints determine valid values for the column. In SQL

Developer, the only constraint you can define at the column level in the Create Table dialog box pagc is the NOT NULL constraint. which rcquircs that a value be included in

the column whenever a row is inserted or updated. Unlike other constraints described in "About Table-Level Constraints" on page 8-8, which can be defined as part of the column definition or part of the table definition, the NOT NULL constraint musi be defined as part of the column definition.

Use a NOT NULL constraint whcn data must be supplicd for a column for the intcgrity

of the database. For example, if all cmployees must bclong to a specific department, then the column that contains the department identifier must be defined with a NOT NULL constraint. However, do not define a column as NOT NULL if the data can be unknown or may not exist whcn rows are added or changed. An example of a column for which you must not use a NOT NULL constraint is the second, optional linę in a mailing address.

The database automatically adds a NOT NULL constraint to the column or columns included in the primary key of a table.