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Null Values on a Column

  

Description

A field is referred to as null if it has not received a value or its value is not clearly identified.

To visually create a null field, display the table in Design View. In the top section, click the column name. In its corresponding Allow Nulls section, check or clear the check box.

Allow Nulls

To specify the nullity of a column using SQL, on the right side of the column creation, type NULL. To specify that the values of the column are required, on the right side, type NOT NULL. If you don't specify NULL or NOT NULL, the column will be created as NULL. Here are examples:

CREATE TABLE Persons
(
    FirstName varchar(20) NULL,
    LastName varchar(20) NOT NULL,
    Gender smallint
);
GO

If the table was already created and it holds some values already, you cannot set the Allow Nulls option on columns that don't have values.

After specify that a column would NOT allow NULL values, if the user tries creating a record but omits to create a value for the column, an error would display. Here is an example:

No row was updated

This error message box indicates that the user attempted to submit a null value for a column. To cancel the action, you can press Esc.

 

 

     
 

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