列1对于所有行都是相同的。如果是，则使用两组过滤器，否则必须找到col1和col4之间的uniq值，并删除空值，使用以下步骤
filter\u one将捕获col1和col4，其中col4不为空
过滤器2将捕获col1，col2，col3。使用连接筛选器\u one&
filter_two，其中filter_two将打印在第1、第2、第3列
第二列在第四个位置，
希望这也能有所帮助
Pig的脚本如下：

Filter_one = foreach Load_Data generate $0 as col1, $3 as col4;
Filter_one_temp =  filter Filter_one by ($1 is not null);
Filter_two = foreach Load_Data generate $0 as col1, $1 as col2, $2 as col3;
Join_filter =  JOIN Filter_two by $0 LEFT, Filter_one_temp by $0;
generetate_output = foreach Join_filter generate $0 as col1, $1 as col2 , $2 as col3,$4 as col4;
store generetate_output into 'dfs_path' using PigStorage(',');

当我存储相同的数据时，delimeter的输出将是

(ABC,34,23,XYZ)
(ABC,12,78,XYZ)
(ABC,4,21,XYZ)
(ABC,22,54,XYZ)
(DEF,32,455,JKL)
(DEF,21,45,JKL)
(DEF,45,687,JKL)
(DEF,232,565,JKL)
(DEF,23,32,JKL)

如果您的需求是将所有值为null或空的记录的col4值更新为xyz，那么您可以使用下面的代码段执行相同的操作

--Load input data
input_data = LOAD 'input.txt' USING PigStorage() AS (Col1:chararray, Col2:int, Col3:int, Col4:chararray);

--Perform operation on each record
input_data = FOREACH input_data GENERATE Col1, Col2, Col3, ((Col4 is null or TRIM(Col4) == '') ? 'XYZ' : Col4) as Col4;

这里假设您保存的是您的输入数据，那么对于每个记录，检查col4值是null还是空的，如果是空的，则用所需的值（xyz）更新它，否则只使用现有的值