...

Subqueries in the FROM clause

SELECT ... FROM (subquery) name ...

...

SELECT t3.col
FROM (
  SELECT a+b AS col
  FROM t1
  UNION ALL
  SELECT c+d AS col
  FROM t2
) t3

Subqueries in the WHERE clause

As of Hive 0.13 some types of subqueries are supported in the WHERE clause. Those are queries where the result of the query can be treated as a constant for IN and NOT IN statements (called uncorrelated subqueries because the subquery does not reference columns from the parent query):

SELECT *
FROM A
WHERE A.a IN (SELECT foo FROM B);
{code:sql}

The other supported type are EXISTS and NOT EXISTS subqueries:
{code:sql}
SELECT A
FROM T1
WHERE EXISTS (SELECT B FROM T2 WHERE T1.X = T2.Y)

There are a few limitations:

• These subqueries are only supported on the right hand side of an expression
• IN/NOT IN subqueries may only select a single column
• EXISTS/NOT EXISTS must have one or more correlated predicates
• References to the parent query are only supported in the WHERE clause of the subqueries