Subquery Syntax
SELECT ... FROM (subquery) name ...
Hive supports subqueries only in the FROM clause. The subquery has to be given a name because every table in a FROM clause must have a name. Columns in the subquery select list must have unique names. The columns in the subquery select list are available in the outer query just like columns of a table. The subquery can also be a query expression with UNION. Hive supports arbitrary levels of sub-queries.
Example with simple subquery:
SELECT col FROM ( SELECT a+b AS col FROM t1 ) t2
Example with subquery containing a UNION ALL:
SELECT t3.col FROM ( SELECT a+b AS col FROM t1 UNION ALL SELECT c+d AS col FROM t2 ) t3