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For complex dBASE indexes, the complexity of the index expression varies according to the way the index is used. The following rules apply when defining complex indexes:

An index value can be up to 100 characters long. The text of the key expression can be up to 220 characters long.

The complex index must be a valid dBASE expression. Note that a single field name is a valid expression.

The expression must evaluate to a character, date, numeric, or float value.

It usually, but not always, contains at least one field name.

For multiple character fields, concatenate, or combine, fields using the plus sign (+), as shown in the following examples:

 LAST_NAME + FIRST_NAME + M_INITIAL

 CUSTOMER + ORDER_NO

You can concatenate fields of different data types by converting them to a single type. In the following example, the key expression concatenates the CUSTOMER_N field, which is a character field, and ORDER_DATE, which is a date field. The DTOS( ) function converts the date value to a character string in the format YYYYMMDD. This order—year first, then month, then day—ensures accurate indexing.

 CUSTOMER_N + DTOS(ORDER_DATE)

For converting number fields, use the STR( ) function. Include the width and number of decimal places of the numeric field(s), to ensure accuracy of the index. For example, suppose you are creating an index that includes a character field LNAME, and a numeric field called AMOUNT that is 10 places wide with 2 decimal places. Use the following syntax:

 LNAME+STR(AMOUNT,10,2)