hadoop - 在 PIG 中一次左外连接超过 2 个关系

Question

我正在尝试在 pig 的单个语句中对 2 个以上的关系执行左外连接。可能吗？

问候哈里什

Answer 1

不幸的是，一步中的多路连接仅适用于内部连接。取自the official documentation :

Usage

...

Outer joins will only work for two-way joins; to perform a multi-way outer join, you will need to perform multiple two-way outer join statements.

因此，在他们添加可能性之前，这不会很快出现(没有开放的 JIRA 正在处理它)，您将需要在 2 个语句中完成:

A = LOAD 'a' AS (a:chararray,b:int);
B = LOAD 'b' AS (a:chararray,b:chararray);
C = LOAD 'c' AS (a:chararray,b:chararray);
D = JOIN A by $0 LEFT OUTER, B BY $0;
E = JOIN D by $0 LEFT OUTER; C BY $0;