[jira] [Created] (SPARK-27912) Improve parser error message for CASE clause

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

Yesheng Ma created SPARK-27912:
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             Summary: Improve parser error message for CASE clause
                 Key: SPARK-27912
                 URL: https://issues.apache.org/jira/browse/SPARK-27912
             Project: Spark
          Issue Type: Sub-task
          Components: SQL
    Affects Versions: 3.0.0
            Reporter: Yesheng Ma


The \{{CASE}} clause is commonly used in SQL queries, but people can forget the trailing {{END}}. When a user queries such a statement, the error message is confusing. For example, the error message for


{code:sql}
SELECT (CASE WHEN a THEN b ELSE c) FROM a;
{code}

is
{code:java}
no viable alternative at input '(CASE WHEN a THEN b ELSE c)'(line 1, pos 33)
{code}
which is misleading.
 

One possible way to fix is to explicitly capture these statements in a grammar rule and print user-friendly error message such as
{code:java}
missing trailing END for case clause
{code}



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