Pig Latin JOIN (inner) 与JOIN (outer)的区别

1、内连接(自然连接): 只有两个表相匹配的行才能在结果集中出现

2、外连接: 包括

（1）左外连接(左边的表不加限制)

（2）右外连接(右边的表不加限制)

（3）全外连接(左右两表都不加限制)

3.  例子

   a.txt

1 2 3                   
4 2 1
8 3 4
4 3 3
7 2 5
8 4 3 

b.txt

2 4
8 9
1 3
2 7
2 9
4 6
4 9

LEFT JOIN

grunt> A = LOAD '/user/mypig/a.txt' AS(a1:chararray,a2:chararray,a3:chararray);
grunt> B= LOAD  '/user/mypig/b.txt' AS(b1:chararray,b2:chararray);
grunt> C = JOIN A BY a1,B BY b1;
grunt> DUMP C;

结果：

(1,2,3,1,3)

(4,2,1,4,6)

(4,2,1,4,9)

(4,3,3,4,6)

(4,3,3,4,9)

(8,3,4,8,9)

(8,4,3,8,9)

LEFT OUTER:

grunt> C = JOIN A BY a1 LEFT OUTER,B BY b1;
grunt> DUMP C;

结果：

(1,2,3,1,3)

(4,2,1,4,6)

(4,2,1,4,9)

(4,3,3,4,6)

(4,3,3,4,9)

(7,2,5,,)

(8,3,4,8,9)

(8,4,3,8,9)

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