拉丁语；这与预期一样有效：
filtered = FILTER records BY age > 27;但这会引发异常（当>>转储过滤时）：
filtered = FILTER records BY records.age > 27;这是一个例外：
java.lang.Exception: org.apache.pig.backend.executionengine.ExecException: ERROR 0: Scalar has more than one row in the output. 1st : (John,Wilk,27,M), 2nd :(Tri,Tim,27,F)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:403)
Caused by: org.apache.pig.backend.executionengine.ExecException: ERROR 0: Scalar has more than one row in the output. 1st : (John,Wilk,27,M), 2nd :(Tri,Tim,27,F)
at org.apache.pig.impl.builtin.ReadScalars.exec(ReadScalars.java:119)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:345)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNextInteger(POUserFunc.java:394)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.getNext(PhysicalOperator.java:322)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.GreaterThanExpr.getNextBoolean(GreaterThanExpr.java:74)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POFilter.getNextTuple(POFilter.java:144)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.runPipeline(PigGenericMapBase.java:282)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:277)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:64)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:763)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:339)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:235)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)两者有什么区别？他们不一样吗？
1条答案
按热度按时间bvn4nwqk1#
不，两个stmt是不同的。
第一个stmt是完全有效的，在这种情况下，pig将遍历每一行并应用filter约束（age>27）。这是使用过滤器stmts的标准方法。
在第二种情况下，你用
dereference operator(.)访问字段，但解引用运算符主要用于访问复杂数据类型（元组、包和Map）值，当使用解引用运算符访问字段时，pig将always expect the scalar output（即，过滤条件后只有一个输出）不幸的是，过滤条件（年龄>27岁）返回more than one matching result，这就是你得到Scalar has more than one row in the output如果你的过滤条件（年龄>27岁）只返回一个输出，那么你的stmt是完全有效的。