hive: NULL值关联与空字符串关联问题

案例:

with tab1 as (SELECt 
		stack(3,
			  '1001',50,
			   '',60,
			  NULL,70
			  ) as (id, score)
	), 
	tab2 as (select 
		stack(3, 
			 '1001', 777, 
			 '', 999, 
			 null, 555) as (id, score)
	)
select a.*, b.* from tab1 a full join tab2 b on a.id = b.id

执行结果:

id	score	id	score
null	70	null	NULL
null	NULL	null	555
	60		999
1001	50	1001	777

总结:
NULL值关联不上 ，但是空字符串会关联到数据