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From sudheeshkatkam <...@git.apache.org>
Subject [GitHub] drill issue #541: DRILL-4673: Implement "DROP TABLE IF EXISTS" for drill to ...
Date Thu, 21 Jul 2016 23:28:31 GMT
Github user sudheeshkatkam commented on the issue:

    tl;dr +1, please open a ticket.
    Moving conversation. Vitalii said:
    > I checked every schema#getTable and found that every method can throw exception only
if something go wrong (permissionError, dataReadError, IOException etc). 
    getTableFromSchema()can not throw any exception, because in this method catch (Exception
e) is used.
    Correct, `catch(Exception e)` is used, but the exception is wrapped in a `DrillRuntimeException`
and re-thrown.
    I think it "happens so" that all plugins are doing the right thing. To explain myself,
there are two cases that I am concerned about:
    1.  `getTableFromSchema` (and underlying `schema#getTable`) throws an exception when a
table does not exist. For example, if the HBase plugin supports dropping tables in the future,
an invalid table name will cause the query to [fail with](https://github.com/apache/drill/blob/master/contrib/storage-hbase/src/main/java/org/apache/drill/exec/store/hbase/DrillHBaseTable.java#L42)
a `TableNotFoundException`, which is exactly the case an exception should not thrown, if `IF
EXISTS` exists.  _For now,_ since hbase schema is not mutable, the [check for schema mutability](https://github.com/apache/drill/pull/541/files#diff-50862f72c560b2d1bd9af36e83019d80R66),
before deleting the table, fails.
    2. `getTableFromSchema` (and underlying `schema#getTable`) does not return `null` for
non-existent tables, and `schema#dropTable` will fail. _For now_, only two schema support
dropping tables: `WorkspaceSchema` and `KuduTables`, and they return `null` for non-existent
tables. The check for schema mutability fails for other schema.
    Overall, it seems there is an unwritten rule (`schema#getTable` should return `null` if
the table does not exist) that should be documented, and HBase plugin should be fixed. AFAIK
other plugins follow this rule.
    +1 for the changes; I think we should track these above issues in another ticket.

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