在级联管道中，什么是SQL而不是IN？

Question

我有两个带有一个公共字段的文件，基于这个字段值，我需要获得第二个文件值。

我该如何在这里添加where条件？

是否有其他管道可供不使用？

File1:

tcno,date,amt
1234,3/10/2016,1000
1234,3/11/2016,400
23456,2/10/2016,1500

File2:

cno,fname,lname,city,phone,mail
1234,first,last,city,1234556,123@123.com

示例代码：

Pipe pipe1 = new Pipe("custPipe");
Pipe pipe2 = new Pipe("tscnPipe");
Fields cJoinField = new Fields("cno");
Fields tJoinField = new Fields("tcno");
Pipe pipe = new HashJoin(pipe1, cJoinField, pipe2, tJoinField,  new OuterJoin());
//HOW TO ADD WHERE CONDITION i.e. CNO IS NULL FROM SECOND FILE
Fields outFields = new Fields("tcno","tdate", "tamt");

我期望输出作为第一文件，最后一行23456,2/10/2016,1500

Answer 1

根据代码中的注释：

//HOW TO ADD WHERE CONDITION i.e. CNO IS NULL FROM SECOND FILE

尝试使用FilterNull。

在HashJoin步骤之后，在代码中添加以下行：

FilterNull filterNull = new FilterNull();
pipe = new Each( pipe, cJoinField, filterNull );

类似于：

Pipe pipe1 = new Pipe("custPipe");
Pipe pipe2 = new Pipe("tscnPipe");
Fields cJoinField = new Fields("cno");
Fields tJoinField = new Fields("tcno");
Pipe pipe = new HashJoin(pipe1, cJoinField, pipe2, tJoinField,  new OuterJoin());

// Filter out those tuples which has cno as null
FilterNull filterNull = new FilterNull();
pipe = new Each( pipe, cJoinField, filterNull );

Fields outFields = new Fields("tcno","tdate", "tamt");