[clickhouse-jdbc] describe SELECT queries to retrieve metadata #1700
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Summary
This is an attempt to reanimate #1434 to enable
getMetadata()
method to return metadata for a preparedSELECT
query that hasn't yet been executed. Also see #1430 .This functionality is needed (among other use-cases) to support query passthrough for clickhouse-connector inside Trino.
Implementation
DESCRIBE (<select>)
is used to retrieve metadata aboutSELECT
query that hasn't yet been executed.Contrary to #1434 the method requires the query to be "recognized" and be
SELECT
, thus removing the ambiguity of supporting different query types. Otherwise it wraps the query insideDESCRIBE ()
clause to build respective metadata object.Additional unit tests were added to address remarks to the original PR.
Checklist
Delete items not relevant to your PR:
cc: @zhicwu , @ebyhr