HiveQL - Union

To apply ORDER BY, SORT BY, CLUSTER BY, DISTRIBUTE BY or LIMIT to an individual SELECT, place the clause inside the parentheses that enclose the SELECT:

SELECT key FROM (SELECT key FROM src ORDER BY key LIMIT 10)subq1
UNION
SELECT key FROM (SELECT key FROM src1 ORDER BY key LIMIT 10)subq2

To apply an ORDER BY, SORT BY, CLUSTER BY, DISTRIBUTE BY or LIMIT clause to the entire UNION result, place the ORDER BY, SORT BY, CLUSTER BY, DISTRIBUTE BY or LIMIT after the last one. The following example uses both ORDER BY and LIMIT clauses:

SELECT key FROM src
UNION
SELECT key FROM src1 
ORDER BY key LIMIT 10