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https://issues.apache.org/jira/browse/FLINK-4241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15516619#comment-15516619
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ASF GitHub Bot commented on FLINK-4241:
---------------------------------------
Github user fhueske commented on the issue:
https://github.com/apache/flink/pull/2529
+1 to merge
> Cryptic expression parser exceptions
> ------------------------------------
>
> Key: FLINK-4241
> URL: https://issues.apache.org/jira/browse/FLINK-4241
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Affects Versions: 1.1.0
> Reporter: Till Rohrmann
> Assignee: Timo Walther
>
> The exceptions thrown when giving wrong SQL syntax to Flink's SQL parser is
> very cryptic and should be improved. For example, the following code snippet:
> {code}
> inputTable.filter("a == 0");
> {code}
> gives the following exception:
> {code}
> Exception in thread "main"
> org.apache.flink.api.table.ExpressionParserException: Could not parse
> expression: [1.4] failure: `-' expected but `=' found
> a == 0
> ^
> at
> org.apache.flink.api.table.expressions.ExpressionParser$.parseExpression(ExpressionParser.scala:355)
> at org.apache.flink.api.table.Table.filter(table.scala:161)
> at
> com.dataartisans.streaming.SimpleTableAPIJob.main(SimpleTableAPIJob.java:32)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.lang.reflect.Method.invoke(Method.java:497)
> at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
> {code}
> From this description it is very hard to understand that {{==}} is not a
> valid operator.
> Another example is:
> {code}
> inputTable.select("*");
> {code}
> which gives
> {code}
> Exception in thread "main"
> org.apache.flink.api.table.ExpressionParserException: Could not parse
> expression: Base Failure
> at
> org.apache.flink.api.table.expressions.ExpressionParser$.parseExpressionList(ExpressionParser.scala:342)
> at org.apache.flink.api.table.Table.select(table.scala:103)
> at
> com.dataartisans.streaming.SimpleTableAPIJob.main(SimpleTableAPIJob.java:33)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.lang.reflect.Method.invoke(Method.java:497)
> at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
> {code}
> I think it would considerably improve user experience if we print more
> helpful parsing exceptions.
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