JOIN

JOIN

Create a new database file by merging records/fields from two work areas

Syntax

      JOIN WITH <xcAlias> TO <xcDatabase>
             FOR <lCondition> [FIELDS <idField list>]

Arguments

WITH <xcAlias> is the name of the work area to merge with records from the current work area. You can specify it either as a literal alias or as a character expression enclosed in parentheses.

TO <xcDatabase> is the name of the target database file specified either as a literal filename or as a character expression enclosed in parentheses.

FOR <lCondition> selects only records meeting the specified condition.

FIELDS <idField list> is the projection of fields from both work areas into the new database file. To specify any fields in the secondary work area, reference them with the alias. If the FIELDS clause is not specified, all fields from the primary work area are included in the target database file.

Description

JOIN creates a new database file by merging selected records and fields from two work areas based on a general condition. JOIN works by making a complete pass through the secondary work area for each record in the primary work area, evaluating the condition for each record in the secondary work area. When the <lCondition> is true (.T.), a new record is created in the target database file using the FIELDS specified from both work areas.

If SET DELETED is OFF, deleted records in both source files (i.e., the two files being JOINed) are processed. However, their deleted status is not retained in the target <xcDatabase>. No record in the target file is marked for deletion regardless of its deleted status in either of the source files.

If SET DELETED is ON, no deleted records are processed in either of the source files. Thus, deleted records do not become part of the target <xcDatabase>. Similarly, filtered records are not processed and do not become part of the target file.

Warning! The number of records processed will be the LASTREC() of the primary work area multiplied by the LASTREC() of the secondary work area. For example, if you have two database files with 100 records each, the number of records JOIN processes is the equivalent of sequentially processing a single database file of 10, 000 records. Therefore, use this command carefully.

Examples

      .  This example joins Customer.dbf to Invoices.dbf to produce
         Purchases.dbf:
         USE Invoices NEW
         USE Customers NEW
         JOIN WITH Invoices TO Purchases;
            FOR Last = Invoices->Last;
            FIELDS First, Last, Invoices->Number, ;
               Invoices->Amount

Seealso

SET RELATION

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