set hive.auto.convert.join = true;

explain
SELECT sum(hash(src1.c1, src2.c4)) 
FROM
(SELECT src.key as c1, src.value as c2 from src) src1
JOIN
(SELECT src.key as c3, src.value as c4 from src) src2
ON src1.c1 = src2.c3 AND src1.c1 < 100;

SELECT sum(hash(src1.c1, src2.c4)) 
FROM
(SELECT src.key as c1, src.value as c2 from src) src1
JOIN
(SELECT src.key as c3, src.value as c4 from src) src2
ON src1.c1 = src2.c3 AND src1.c1 < 100;