SELECTINDEX()

The SELECTINDEX statement creates a select list from an alternate key index entry.

Format

SELECTINDEX index.name {, value} FROM file.var {TO list.no}

where

index.name

is the name of the alternate key index to be processed.

value

is the value to be located in the index.

file.var

is the file variable associated with an open file.

list.no

is the select list number of the list to be created. If omitted, select list zero is used.

If the value is omitted, the SELECTINDEX statement constructs a select list containing all the values of the index identified by index.name. If the value is included, the SELECTINDEX statement constructs a select list containing keys of records for which the index indentifed by index.name has the given value.

Thus, in a file of orders with an index on the customer number field, the first form would return a list of customers referenced by the orders file and the second form would return a list of orders for a specific customer.

The STATUS() function returns zero if the SELECTINDEX is successful, non-zero if it fails because the index does not exist. Selecting records for a value that is not present in the index will return an empty list.

]The @SELECTED variable is set to the number of entries in the returned list.

The SELECTINDEX operation leaves the internal index pointer used by the SELECTLEFT and SELECTRIGHT statements positioned at the item that has been located or, if not found, at the position where such an item would go.

Use of this statement inside a transaction will not reflect any uncommitted updates to the file.

To understand the order in which items are returned by SELECTINDEX, consider a file keyed by customer number for which there is an index on a field that contains the dates of orders placed by the customer. The index will have an entry for each date and each of these entries will hold a list of customers placing orders on that date. The order of the indexed values (order dates, left column in the diagram below) will be sorted left or right aligned according to the format code in the dictionary entry for the date field. The customer numbers stored for each date (a single line from the right column in the diagram below) will be sorted according to the format code in the dictionary entry for the @ID item in the customers file.

index

Examples

SELECTINDEX 'CUST.NO' FROM ORDERS.FILE TO 7

LOOP

READNEXT CUST.NO FROM 7 ELSE EXIT

CRT CUST.NO

SELECTINDEX 'CUST.NO', CUST.NO FROM ORDERS.FILE

LOOP

READNEXT ORDER.NO ELSE EXIT

CRT ORDER.NO
REPEAT

REPEAT

This program builds a select list of all the customers referenced by the orders file as list 7. The inner loop then constructs a list of the order numbers for each customer in turn.