Determines how null values are supported by the ALTER TABLE, CREATE TABLE and INSERT - SQL commands.

SET NULL ON | OFF

Parameters

ON

Specifies that all columns in a table created with ALTER TABLE and CREATE TABLE will allow null values. You can override null value support for columns in the table by including the NOT NULL clause in the columns' definitions.

Also, specifies that INSERT - SQL will attempt to insert null values into any columns not included in the INSERT - SQL VALUE clause. INSERT - SQL can successfully insert null values only into columns that allow null values.

Note
If you add support for null values to one or more columns in a table, the limit on the number of columns for that table is reduced from 255 to 254.

OFF

(Default) Specifies that all columns in a table created with ALTER TABLE and CREATE TABLE will not allow null values. You can designate null value support for columns in ALTER TABLE and CREATE TABLE by including the NULL clause in the columns' definitions.

Also specifies that INSERT - SQL will insert blank values into any columns not included in the INSERT - SQL VALUE clause.

Remarks

Example

The following example demonstrates how SET NULL affects support for null values. The first table, employee, is created with SET NULL ON, so its fields support null values. REPLACE is used to place a null value in the cLastName field. The second table, staff, is created with SET NULL OFF, so its fields do not support null values. REPLACE is used to place zero in the cLastName field.

Copy Code

CLOSE DATABASES SET NULL ON && Fields will support null values CREATE TABLE employee (cLastName C(20), ySalary Y(12,2)) APPEND BLANK && Add a new blank record REPLACE cLastName WITH .NULL. && cLastName supports null values SET NULL OFF && Fields will not support null values CREATE TABLE staff (cLastName C(20), ySalary Y(12,2)) APPEND BLANK && Add a new blank record REPLACE cLastName WITH 0 && Doesn't support null values

See Also