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SAP Sybase SQL Anywhere 16.0 » SQL Anywhere Server - Database Administration » SQL Anywhere database connections » Database file types » Database creation » Column data type considerations


NULL and NOT NULL columns

If the column value is mandatory for a row, you define the column as being NOT NULL. Otherwise, the column is allowed to contain the NULL value, which represents no value. The default is to allow NULL values, but you should explicitly declare columns NOT NULL unless there is a good reason to allow NULL values.

The sample database has a table called Departments, which has columns named DepartmentID, DepartmentName, and DepartmentHeadID. Its definition is as follows:

Column Data type Size NULL/NOT NULL Constraint
DepartmentID integer NOT NULL Primary key
DepartmentName char 40 NOT NULL None
DepartmentHeadID integer NULL Foreign key

If you specify NOT NULL, a column value must be supplied for every row in the table.

 See also