[jira] [Created] (CALCITE-2982) SqlItemOpeator should throw understandable exception message for incorrect field type

["pengzhiwei (JIRA)" <ji...@apache.org>]

pengzhiwei created CALCITE-2982:
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             Summary: SqlItemOpeator should throw understandable exception message for incorrect field type
                 Key: CALCITE-2982
                 URL: https://issues.apache.org/jira/browse/CALCITE-2982
             Project: Calcite
          Issue Type: Bug
          Components: core
            Reporter: pengzhiwei
            Assignee: pengzhiwei
             Fix For: 1.20.0


In the follow sql:
{code:java}
sql("select name[0] from dept").ok();
{code}
_name_ is a field of _VARCHAR_ type, the follow exception message is thrown out:
{code:java}
java.lang.AssertionError: VARCHAR
at org.apache.calcite.sql.fun.SqlItemOperator.getChecker(SqlItemOperator.java:109)
at org.apache.calcite.sql.fun.SqlItemOperator.checkOperandTypes(SqlItemOperator.java:91)
at org.apache.calcite.sql.SqlOperator.validateOperands(SqlOperator.java:432)
at org.apache.calcite.sql.SqlOperator.deriveType(SqlOperator.java:516)
at org.apache.calcite.sql.validate.SqlValidatorImpl$DeriveTypeVisitor.visit(SqlValidatorImpl.java:5607)
at org.apache.calcite.sql.validate.SqlValidatorImpl$DeriveTypeVisitor.visit(SqlValidatorImpl.java:5594)
at org.apache.calcite.sql.SqlCall.accept(SqlCall.java:139)
{code}
The exception message is hard to understand  for user. I think a message like "Cannot apply item opeator to VARCHAR type for filed "name"  at line xx column xx " is more friendly to the user.



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