hadoop - 在 Hadoop Pig 中加入和分组

Question

经常看到有人在使用 group by 和 join 来解决同样的问题，假设我有一个学生表和分数表，想找到与类(class)分数相关的学生姓名。看来我们可以通过使用 join 或使用 group by 来解决这个问题？想知道这两种解决方案的优缺点。发布数据结构和代码如下。谢谢。

table students:

student ID, student name, student email address

score table:

student ID, course ID, score

student_scores = group students by (studentId) inner, scores by (studentId);

student_scores = join students by student Id, scores by studentId;

Answer 1

在 Pig Latin 手册中关于 Join它说:

Note the following about the GROUP/COGROUP and JOIN operators:

The GROUP and JOIN operators perform similar functions. GROUP creates a nested set of output tuples while JOIN creates a flat set of output tuples.
The GROUP/COGROUP and JOIN operators handle null values differently (see Nulls and JOIN Operator).

不知道是不是优缺点，但它们是不同的