Pig Join-如何使用多个字段连接两个表，其中键中的一个字段是可选的？

问题：猪初学者-下面是我的两个输入表

Table 1: Contain 3 columns (VID, TID and USID)
v1 TID101 US101 
v2 TID102 
v3 TID103 
v4 TID104 US104 
v5        US105 
v6        US106 

我想连接表1和表2，并得到如下输出：

Expected Output:
v1 TID101 US101 p1
v2 TID102       p2
v3 TID103       p3
v4 TID104 US104 p4
v5        US105 p5

a= JOIN table1 BY (TID, USID), table2 BY (TID, USID);
b= FOREACH a GENERATE table1::vID, table1::TID, table1::USID, table2::PID;

我尝试了如下的内部连接：

Expected Output:
v1 TID101 US101 p1
v2 TID102       p2
v3 TID103       p3
v4 TID104 US104 p4
v5        US105 p5

a= JOIN table1 BY (TID, USID), table2 BY (TID, USID);
b= FOREACH a GENERATE table1::vID, table1::TID, table1::USID, table2::PID;

但我只得到以下输出：

---

我可以尝试左外连接，但我觉得当我通过多个键连接时，两个键都被认为是必须连接的，我不能有“或”条件。如果table1记录包含USID或TID，我只想从table2中获取PID。我不确定我错过了什么，并且有兴趣了解达到预期输出的最佳方法。请帮忙

在单个列上进行连接，合并结果并区分最终关系

PigScript

A = LOAD 'test1.txt' USING PigStorage('\t') as (a1:chararray,a2:chararray,a3:chararray);
B = LOAD 'test2.txt' USING PigStorage('\t') as (b1:chararray,b2:chararray,b3:chararray);

A2 = JOIN A BY (a2),B by (b2);
A3 = JOIN B BY (b3),A by (a3);

C = FOREACH A2 GENERATE A::a1,A::a2,A::a3,B::b1;
D = FOREACH A3 GENERATE A::a1,B::b2,B::b3,B::b1;

E = UNION C,D;
E1 = DISTINCT E;

DUMP E1;

输出

A = LOAD 'test1.txt' USING PigStorage('\t') as (a1:chararray,a2:chararray,a3:chararray);
B = LOAD 'test2.txt' USING PigStorage('\t') as (b1:chararray,b2:chararray,b3:chararray);

A2 = JOIN A BY (a2),B by (b2);
A3 = JOIN B BY (b3),A by (a3);

C = FOREACH A2 GENERATE A::a1,A::a2,A::a3,B::b1;
D = FOREACH A3 GENERATE A::a1,B::b2,B::b3,B::b1;

E = UNION C,D;
E1 = DISTINCT E;

DUMP E1;

---

谢谢。这很有帮助