How to Index on Numbers in a Character Field

• Microsoft Visual FoxPro for Windows, version 3.0
• Microsoft FoxPro for Windows, versions 2.5, 2.5a, and 2.5b
• Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, and 2.5b
• Microsoft FoxPro for Macintosh, version 2.5b

SYMPTOMS

If a character field is made up of numbers and the database is indexed on this field, the numbers are not in the expected order.

NOTE: This article assumes that all numbers must be positive.

CAUSE

In character fields, each character is evaluated one at a time from left to right. Therefore, the order may not match that of a numeric field.

RESOLUTION

To get the character field in numerical order, you must create an index key using the PADL() function. The PADL() function will put a character to the left of the character expression in order to make the digits right aligned.

Example

1. In your database, create a character field called IDNUM that has a width of 10 and is composed entirely of numbers.

2. In the Command window, type:

         INDEX ON PADL(ALLTRIM(IDNUM),10,"0") TAG IDSORT
   

   This command will create a tag call IDSORT that will shift all the characters to the right as far as the length of the field.

3. In the Command window, issue the following command in order to index the database on the IDSORT tag:

         SET ORDER TO TAG IDSORT
   

MORE INFORMATION

To illustrate the behavior described in the "Symptoms" section above, suppose you have a character field called IDNUM that has a width of 10 and is made up of all numbers. The following table shows how the numbers will be ordered.

   IDNUM order      IDNUM order when table
   on input         is indexed on IDNUM
   ---------------------------------------

        2                    1
        30                   10
        1                    12
        10                   122
        12                   2
        200                  200
        122                  30