hadoop - 使用 pig latin 选择不同的计数

Question

我需要有关此 pig 脚本的帮助。我只是得到一个记录。我正在选择 2 列并对另一列进行计数(不同)，同时还使用 where like 子句来查找特定描述 (desc)。

这是我正在尝试编写的带有 pig 的 sql。

 /*
    For example in sql:
    select domain, count(distinct(segment)) as segment_cnt
    from table
    where desc='ABC123'
    group by domain
    order by segment_count desc;
    */

    A = LOAD 'myoutputfile' USING PigStorage('\u0005')
            AS (
                domain:chararray,
                segment:chararray,
                desc:chararray
                );
B = filter A by (desc=='ABC123');
C = foreach B generate domain, segment;
D = DISTINCT C;
E = group D all;
F = foreach E generate group, COUNT(D) as segment_cnt;
G = order F by segment_cnt DESC;

Answer 1

您可以对每个域进行 GROUP，然后使用 nested FOREACH 计算每个组中不同元素的数量。语法:

D = group C by domain;
E = foreach D { 
    unique_segments = DISTINCT C.segment;
    generate group, COUNT(unique_segments) as segment_cnt;
};