Part 3 of "Keeping Your Information Accurate in Access 2003 and Access 2002": Using the field size property to restrict data (311169)

MORE INFORMATION

You can set the Field Size property for the Text, Number, and AutoNumber data types. This property restricts the number of characters you can enter in a text field and the size of numbers that can be entered in a Number or AutoNumber field. For text fields, the Field Size property can be set to any number from 0 to 255. AutoNumber fields can be set to Long Integer or Replication ID. They are set to Long Integer by default. Number fields can be set to any of the following values:

   Setting         Description
   ------------------------------------------------------------------------

   Byte            Stores numbers from 0 to 255 (no fractions).

   Integer         Stores numbers from -32,768 to 32,767 (no fractions).
 
   Long Integer    (The default.) Stores numbers from -2,147,483,648 to
                   2,147,483,647 (no fractions).

   Single          Stores numbers from -3.402823E38 to -1.401298E-45 for 
                   negative values and from 1.401298E-45 to 3.402823E38 
                   for positive values.

   Double          Stores numbers from -1.79769313486231E308 to
                   -4.94065645841247E-324 for negative values and from 
                   1.79769313486231E308 to 4.94065645841247E-324 for 
                   positive values.

   Decimal         Stores numbers from -10^28 -1 through 10^28 -1 (.mdb).

   Replication ID  Globally unique identifier (GUID). A 16-byte field used
                   in an Access database to establish a unique identifier
                   for replication. GUIDs are used to identify replicas, 
                   replica sets, tables, records, and other objects. In an
                   Access database, GUIDs are referred to as Replication 
                   IDs.

By setting the Field Size property to a value that allows the largest valid entry, you prevent the user from entering certain types of invalid information. If you try to type more characters in a text field than the number allowed by the Field Size setting, Access beeps and refuses to accept the entry. Likewise, a value that is below or above the limits of a number field is rejected when you try to move out of the field.

In this exercise, you will change the Field Size property for several fields to see what impact this has on data already in the table and on new data you enter. Follow these steps:

1. Open the Field Test database that you created in Part 2 of this series of articles. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

   311168 ACC2002: Keeping Your Information Accurate: Part 2: Using the Data Type to Restrict Data

2. Open the Field Property Test table in Design view.
3. Click in the TextField row, and in the Field Properties section, change the Field Size property to 12.
4. Click in the NumberField row, click the Field Size property, click its down arrow, and then click Byte in the drop-down list.
   
   You have just restricted the number of characters that can be entered in the text field to 12 and the values that can be entered in the number field to the range 0 to 255.
5. Click the View button to return to Datasheet view, clicking Yes when prompted to save the table.
   
   The table contains data that doesn't fit these new property settings, so Access displays a warning, that some data might be lost:
   
   
6. Click Yes to acknowledge the risk, and click Yes again to accept the deletion of the contents of one field.
   
   Your datasheet now looks like this:
   
   
   
   TextField now contains only 12 characters, rather than the 32 you entered. The other 20 characters have been permanently deleted. NumberField is empty. Because it is now limited to whole numbers from 0 through 255, the value of 500 that you entered has been deleted.
7. Type 2.5 as the NumberField entry, and press ENTER to see what happens.
   
   The number is rounded down to the nearest whole number.
8. Save and close the table, and then close the database.

ADDITIONAL RESOURCES

For additional information, click the following article numbers to view the articles in the Microsoft Knowledge Base: