UNION

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UNION (set1; set2; resultSet)

UNION creates a set that contains all records from set1 and set2. The following table shows all possible results of a set Union operation.

The result of a Union operation is depicted here. The shaded area is the result set.

The resultSet is created by UNION. The resultSet replaces any existing set having the same name, including set1 and set2. Both set1 and set2 must be from the same table. The resultSet belongs to the same table as set1 and set2. The current record for the resultSet is the current record from Set1.

4D Server: In Client/Server, interprocess and process sets are maintained on the server machine, while local sets are maintained on the client machines. UNION requires the three sets to be on the same machine. Consequently, all or none of the sets must be local. See the discussion 4D Server and Sets in the 4D Server Reference manual for more information.

This example adds records to a set of best customers. The records are displayed on screen with the first line. After the records are displayed, a set of the best customers is loaded from disk, and any records that the user selected (the set named "UserSet") are added to the set. Finally, the new set is saved on disk:

   ALL RECORDS ([Customers])  ` Select all the customers 
   DISPLAY SELECTION ([Customers])  ` Display all the customers in a list 
   LOAD SET ("$Best"; "$SaveBest")  ` Load the set of best customers 
   UNION ("$Best"; "UserSet"; "$Best")  ` Add any selected to the set 
   SAVE SET ("$Best"; "$SaveBest")  ` Save the set of best customers 

DIFFERENCE, INTERSECTION.