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Programming Interfaces
Data Management : Database Access : Joining tables : Implementing other outer joins
Implementing other outer joins
In addition to left outer joins, there are right and full outer joins. A right outer join reverses the join order for the same tables joined with a left outer join. In ABL, you can implement a right outer join by doing a left outer join with the tables in reverse order, but leaving the order of displayed fields the same as for the left outer join. Thus, the Unknown value (?) from the right side appear on the left side of each displayed row, as if the tables were joined from right to left.
A full outer join combines the results of a left and right outer join into a single join. This is rarely used, but you can implement a full outer join by building one temporary table from the results of both a left and right outer join. For more information on temporary tables, see OpenEdge Getting Started: ABL Essentials.