Support consistency level statements

[kornilova203]

This MR supports CQL shell consistency statements https://docs.datastax.com/en/cql-oss/3.x/cql/cql_reference/cqlshConsistency.html

CONSISTENCY [level] and CONSISTENCY

It's convenient to have an option to change consistency level from cql instead of changing jdbc parameters and opening new connection

Implementation of ListResultSet is basic

[maximevw]

Hello @kornilova203

Thanks again for your contributions!

This feature is interesting. But, before deep-diving into this review, I'd like to discuss some points globally:

• If I understand well, the ListResultSet is a basic implementation of ResultSet to handle results programmatically produced by the GetConsistencyLevelExecutor. But in this case, maybe, we could reuse this: https://github.com/ing-bank/cassandra-jdbc-wrapper/blob/35e47fecfdde045ae99223df86beef7f6f83075f/src/main/java/com/ing/data/cassandra/jdbc/CassandraMetadataResultSet.java#L190-L193 I used this to manually build MetadataResultSets. A very simple example is available here: https://github.com/ing-bank/cassandra-jdbc-wrapper/blob/35e47fecfdde045ae99223df86beef7f6f83075f/src/main/java/com/ing/data/cassandra/jdbc/metadata/CatalogMetadataResultSetBuilder.java#L56 What do you think about it?
• The added tests all fail with the error java.sql.SQLException: No such column consistency_level
• Instead of looping on all the available custom executors to check if the query should potentially executed by this executor, we could use a single pattern CONSISTENCY( \\w+)? and if there is a matching group, use SetConsistencyLevelExecutor, otherwise use GetConsistencyLevelExecutor. Note that the statement should not contain anything else but CONSISTENCY <level> when this keyword is present.
• This implementation only supports isolated statements with CONSISTENCY <level> only. So, it's not possible to do something like this (currently supported by doExecute method), for example:

  CONSISTENCY QUORUM;
  UPDATE ...;
  UPDATE ...;
  CONSISTENCY LOCAL_QUORUM;
  UPDATE ...;

  However, I think it's clearly an improvement, not a priority for now.

[maximevw]

Thank you @kornilova203 for fixing the tests. When you'll have time, I'll let you discuss my other comments, especially the first and third points of the list.

[kornilova203]

@maximevw, thanks a lot for the review! Those all are fair points But I unfortunately don't have enough time to work on this branch at the moment, so I'll just close the review

[maximevw]

Ok, no problem @kornilova203. I keep the idea and I'll try to re-implement this for the next version, based on your work.

[maximevw]

For information @kornilova203, this has been implemented in the commit https://github.com/ing-bank/cassandra-jdbc-wrapper/commit/26d59a09d5668fa93ca79a57c8314b3e30a99665. This could be re-used as a basis to implement other interesting commands in the future:

• SERIAL CONSISTENCY <level>
• SOURCE <file>
• COPY FROM / TO <csv_file>