UNION operation

The UNION clause specifies a combination of the output of two subqueries. The two queries must return the same number of elements and compatible types. For the purposes of UNION, all Enterprise JavaBeans (EJB) types in the same inheritance hierarchy are considered compatible. UNION requires that equality be defined for the element types.

query_expression := query_term [UNION [ALL] query_term]*

query_term :=  {select_clause_dynamic  from_clause  [where_clause] 
 [group_by_clause] [having_clause] } | (query_expression) } 

You cannot use dependent value objects with UNION.

UNION ALL combines all results together in a single collection.

UNION combines results but eliminates duplicates.

If ORDER BY is used together with UNION, the ORDER BY must refer to selection expression using integer numbers.

Examples: UNION operation

 select e from EmpBean e union all select m from DeptBean d, in(d.mgr) m

 select e from EmpBean e union all select d from DeptBean d

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