Apache pig 如何计算pig中不同别名的数据减法？

现在我想计算：count_c-count_b-count_a。如何在PIG脚本中实现这一点？

您需要将三个别名连接在一起，为此您需要一个公共字段来连接。假设它们都是单记录别名，您可以创建一个字段n来加入：

dump count_a;
(10)

dump count_b;
(20)

dump count_c;
(30)

然后您可以通过公共字段n加入a&b&c all：

prep_a = FOREACH count_a GENERATE 1 AS n, a; 
prep_b = FOREACH count_b GENERATE 1 AS n, b; 
prep_c = FOREACH count_c GENERATE 1 AS n, c; 

然后最后计算最终结果：

ab = JOIN prep_a by n FULL, prep_b by n;
abc = JOIN ab by prep_a::n FULL, prep_c by n;

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由于您只是在进行常规连接，不必担心键是否存在，因此可以在一条语句中完成所有操作：

abc=join prep_a BY n，prep_b BY n，prep_c BY n
result = FOREACH abc GENERATE (c - b - a) AS result;