[<<Previous Entry] [^^Up^^] [Next Entry>>] [Menu] [About The Guide]
 Specify conditions for ordering

     ORDCOND([FOR <lCondition>]
        [ALL] [WHILE <;lCondition>]
        [EVAL <bBlock> [EVERY <nInterval>]]
        [RECORD <nRecord>] [NEXT <nNumber>]
        [REST] [DESCENDING])


     FOR <lCondition> specifies the conditional set of records on which
     to create the order.  Only those records that meet the condition are
     included in the resulting order.  <lCondition> is an expression that may
     be no longer than 250 characters under the DBFNTX and DBFNDX drivers.
     The maximum value for these expressions is determined by the RDD.  The
     FOR condition is stored as part of the order bag and used when updating
     or recreating the index using the ORDCREATE() or ORDREBUILD() functions.
     Duplicate key values are not added to the order bag.

     Drivers that do not support the FOR condition produce an "unsupported"

     The FOR clause provides the only scoping that is maintained for all
     database changes.  All other scope conditions create orders that do not
     reflect database updates.

     ALL specifies all orders in the current or specified work area.  ALL
     is the default scope for ORDCOND().

     WHILE <lCondition> specifies another condition that must be met by
     each record as it is processed.  As soon as the record is encountered
     that causes the condition to fail, the ORDCREATE() function terminates.
     If a WHILE clause is specified, the data is processed in the controlling
     order.  The WHILE condition is transient (i.e., it is not stored in the
     file, not used for index updates, and not used for index updates and
     ORDREBUILD() purposes).  The WHILE clause creates temporary orders, but
     these orders are not updated.

     Drivers that do not support the WHILE condition produce an "unsupported"

     Using the WHILE clause is more efficient and faster than using the FOR
     clause.  The WHILE clause only processes data for which <lCondition> is
     true from the current position.  The FOR clause, however, processes all
     data in the data source.

     EVAL <bBlock> evaluates a code block every <nInterval>, where
     <nInterval> is a value specified by the EVERY clause.  The default value
     is 1.  This is useful in producing a status bar or odometer that
     monitors the indexing progress.  The return value of <bBlock> must be a
     logical data type.  If <bBlock> returns false (.F.), indexing halts.

     EVERY <nInterval> is a clause containing a numeric expression that
     modifies how often <bBlock> is EVALuated.  The EVERY option of the EVAL
     clause offers a performance enhancement by evaluating the condition for
     every nth record instead of evaluating every record ordered.  The EVERY
     keyword is ignored if you specify no EVAL conditions.

     RECORD <nRecord> specifies the processing of the specified record.

     NEXT <nNumber> specifies the portion of the database to process.  If
     you specify NEXT, the database is processed in the controlling order for
     the <nNumber> number of identities.  The scope is transient (i.e., it is
     not stored in the order and not used for ORDREBUILDing purposes).

     REST specifies the processing of all records from the current
     position of the record pointer to the end of file (EOF).

     DESCENDING specifies that the keyed pairs be sorted in decreasing
     order of value.  If you create a DESCENDING index, you will not need to
     use the DESCEND() function during a SEEK.  DESCENDING is an attribute of
     the file, where it is stored and used for ORDREBUILDing purposes.


     ORDCOND() is designed to set up the conditions for creating a new order
     (using the ORDCREATE() function) or rebuilding an existing order (using
     the ORDREBUILD() function).  Do not use the ORDCOND() function if you
     wish to create or rebuild an entire index file; it is only used for
     setting particular conditions for the order.

     ORDCREATE() or ORDREBUILD() should be used immediately following the
     ORDCOND() function.

     If the DESCENDING clause is not specified, the order is then assumed to
     be ascending.

     The EVAL clause lets you specify a code block to be evaluated as each
     record is placed in the order.  The EVERY clause lets you modify how
     often <bBlock> is called.  Instead of evaluating each record as it is
     placed in the order, evaluation only occurs as every <nInterval> records
     are placed in the order.  This can be used, for example, to create a
     gauge that displays how far the ORDCREATE() or ORDREBUILD() has
     progressed so far.

     The FOR clause provides the only order scoping that is permanent and
     that can be maintained across the life of the application.  The string
     passed as the FOR condition is stored within the order for later use in
     maintaining the order.  Though only accessing part of the database,
     orders created using this clause exist as long as the database is
     active.  The FOR clause lets you create maintainable scoped orders.

     The WHILE, NEXT, REST, and RECORD clauses process data from the current
     position of the database cursor in the default or specified work area.
     If you specify these clauses, the order list remains open and the active
     order is used to organize the database while it is being created.  These
     clauses let you create temporary (non-maintainable) orders.  orders
     created using these clauses contain records in which <lCondition> is
     true(.T.) at the location of the record pointer.


     .  The following example creates a conditional order based on a
        FOR clause.  This index contains only records whose field TransDate
        contains a date greater than or equal to January 1, 1992:

        USE Invoice NEW
        ORDCOND(FOR (Invoice->TransDate >= CTOD
        ORDCREATE("InvDate" , , "Invoice->TransDate")

     .  The following example creates an order that calls a routine,
        "MyMeter," during its creation:

        USE Invoice NEW
        ORDCREATE("Invoice" , , "Invoice->Customer")

This page created by ng2html v1.05, the Norton guide to HTML conversion utility. Written by Dave Pearson