我已经编写了这个pig脚本，它在0.12.0版本上运行得很好，但在0.11.1版本上无法运行我无法确定真正缺少的是什么。
data = LOAD '<file_name>' USING PigStorage(',') AS
(Year,Month:int,DayofMonth,DayOfWeek,DepTime,CRSDepTime,ArrTime,CRSArrTime,UniqueCarrier,
FlightNum,TailNum,ActualElapsedTime,CRSElapsedTime,AirTime,ArrDelay:int,DepDelay,Origin,
Dest,Distance,TaxiIn,TaxiOut,Cancelled,CancellationCode,Diverted,CarrierDelay,
WeatherDelay,NASDelay,SecurityDelay,LateAircraftDelay);
A = FILTER data BY (ArrDelay > 0);
X = GROUP A BY (Dest, Year,
(
Case
when Month>2 AND Month<6 THEN 'SPRING'
when Month>5 AND Month<9 THEN 'SUMMER'
when Month>8 AND Month<12 THEN 'FALL'
when Month==12 OR (Month<3 AND Month>0) THEN 'WINTER'
END
)
);
Y = FOREACH X GENERATE group.Dest, group.Year, group.$2, SUM(A.ArrDelay);
STORE Y INTO 'myoutput';
以下是运行脚本时出现的异常。
Pig Stack Trace
---------------
ERROR 1200: <file DelayBySeasonPerYear.pig, line 7, column 16> Syntax error, unexpected symbol at or near 'Dest'
org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1000: Error during parsing. <file DelayBySeasonPerYear.pig, line 7, column 16> Syntax error, unexpected symbol at or near 'Dest'
at org.apache.pig.PigServer$Graph.parseQuery(PigServer.java:1607)
at org.apache.pig.PigServer$Graph.registerQuery(PigServer.java:1546)
at org.apache.pig.PigServer.registerQuery(PigServer.java:516)
at org.apache.pig.tools.grunt.GruntParser.processPig(GruntParser.java:991)
at org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:412)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:194)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:170)
at org.apache.pig.tools.grunt.Grunt.exec(Grunt.java:84)
at org.apache.pig.Main.run(Main.java:604)
at org.apache.pig.Main.main(Main.java:157)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.hadoop.util.RunJar.main(RunJar.java:160)
Caused by: Failed to parse: <file DelayBySeasonPerYear.pig, line 7, column 16> Syntax error, unexpected symbol at or near 'Dest'
at org.apache.pig.parser.QueryParserDriver.parse(QueryParserDriver.java:235)
at org.apache.pig.parser.QueryParserDriver.parse(QueryParserDriver.java:177)
at org.apache.pig.PigServer$Graph.parseQuery(PigServer.java:1599)
... 14 more
CASE最近才在0.12版本中实现。它在0.11中不可用。
参见：
- https://issues.apache.org/jira/browse/PIG-3268（注意修复版本0.12）
- http://hortonworks.com/blog/announcing-apache-pig-0-12/（关于0.12中的新功能的博客文章，其中之一是
CASE）
建议的解决方案：
编写一个UDF，该UDF接受Month值，然后返回一个带有写出的季节的chararray。然后，在FILTER之后的FOREACH语句中使用这个UDF。
...
A = FILTER data BY (ArrDelay > 0);
A = FOREACH A GENERATE MySeasonUDF(Month) as Season, Dest, Year, ArrDelay;
X = GROUP A BY (Dest, Year, Season);
...