[FLINK-4241] Cryptic expression parser exceptions

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.1.0
• Fix Version/s: 1.2.0
• Component/s: Table SQL / API
• Assignee: Timo Walther
• Reporter: Till Rohrmann
• Created: 21/Jul/16 13:29
• Updated: 26/Sep/16 17:13
• Resolved: 26/Sep/16 17:13

Description

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:

inputTable.filter("a == 0");

gives the following exception:

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)

From this description it is very hard to understand that == is not a valid operator.

Another example is:

inputTable.select("*");

which gives

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)

I think it would considerably improve user experience if we print more helpful parsing exceptions.

Issue Links

• links to: GitHub Pull Request #2529