功能：将两个表中的 同样的字段拼接到一起

測试：

create external table IF NOT EXISTS temp_uniontest_ta

(

a1 string,

a2 string

)

partitioned by (dt string)

row format delimited fields terminated by '\t'

stored as textfile;

ALTER TABLE temp_uniontest_ta ADD IF NOT EXISTS PARTITION (dt = '2014-10-13') location '/temp/unionTest/ta/';

a1	a2	2014-10-13

b1	b2	2014-10-13

c1	c2	2014-10-13

create external table IF NOT EXISTS temp_uniontest_tb

(

a1 string,

a2 string

)

partitioned by (dt string)

row format delimited fields terminated by '\t'

stored as textfile;

ALTER TABLE temp_uniontest_tb ADD IF NOT EXISTS PARTITION (dt = '2014-10-13') location '/temp/unionTest/tb/';

d1	d2	2014-10-13

e1	e2	2014-10-13

select * from

(

select a1,a2 from temp_uniontest_ta where dt = '2014-10-13'

union all

select a1,a2 from temp_uniontest_tb where dt = '2014-10-13'

)tmp;

a1	a2

b1	b2

c1	c2

d1	d2

e1	e2