apache-pig - 如何计算猪中不同别名的数据减法？

Question

dump count_a;
(10)

dump count_b;
(20)

dump count_c;
(30)

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

Answer 1

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 加入：

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; 

然后你可以通过公共字段 n 加入 a & b & c all：

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

然后最后计算最终结果：

result = FOREACH abc GENERATE (c - b - a) AS result;