SQL Language Reference SQL Queries and Subqueries 9 SQL Queries and Subqueries This chapter describes SQL queries and subqueries. This chapter contains these sections: About Queries and Subqueries Creating Simple Queries Hierarchical Queries The UNION [ALL], INTERSECT, MINUS Operators Sorting Query Results Joins Using Subqueries Unnesting of Nested Subqueries Selecting from the DUAL Table Distributed Queries