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From "Fabian Hueske (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-7217) Give hints about unsupported SQL / Table API features.
Date Tue, 18 Jul 2017 08:15:00 GMT
Fabian Hueske created FLINK-7217:

             Summary: Give hints about unsupported SQL / Table API features.
                 Key: FLINK-7217
                 URL: https://issues.apache.org/jira/browse/FLINK-7217
             Project: Flink
          Issue Type: Improvement
          Components: Table API & SQL
            Reporter: Fabian Hueske

The Table API and SQL do not support every type of query. While being valid SQL, we cannot
translate certain queries into execution plans. Especially, the supported syntax of streaming
queries is limited and will probably always be limited.

Therefore it is important to explain a user why a query could not be translated. The problem
here is that we need to wait for the optimizer to explore the full search space and apply
all transformation rules before we can tell the user that the query could not be translated.
Hence, we cannot simply throw an exception if a rule cannot be applied, because another rule
might succeed. If we throw an exception in the optimizer, we would kill the exploration and
miss a valid plan. However, after the optimizer failed, we are missing the complete context
and cannot provide valuable feedback beyond "query uses an unsupported feature".

We should try to improve the situation and provide better feedback to users. One approach
would be that rules collect possible reasons why they could not be applied and these reasons
are returned to the user when the translation fails.

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