6.2. Set Operators
Set operators combine the results of two or more queries into a single query result. The set operators in Oracle are UNION, UNION ALL, INTERSECT, and MINUS.
All of the set operators have the same precedence. To override the default left-to-right evaluation, use parentheses to group SELECT statements that you want evaluated first.
6.2.1. UNION and UNION ALL
The UNION operator will combine two query result sets into a single result set, sorted by the first column of the SELECT clause for both queries. The syntax for using UNION is very straightforward: Two queries that can otherwise stand alone are combined with the keyword UNION. The first query does not need a semicolon; the entire SQL statement is terminated by a single ...
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