[GitHub] john-bodley opened a new pull request #5517: [get_df] Updating multi-statement logic

[GitBox <gi...@apache.org>]

john-bodley opened a new pull request #5517: [get_df] Updating multi-statement logic
URL: https://github.com/apache/incubator-superset/pull/5517
 
 
   This PR fixes an issue we've been running into with multi-statements in Presto which is asynchronous. When using the cursor associated with a raw connection using multiple statements in a synchronous manner, i.e.,  
   ```
   cursor = engine.raw_connection().cursor()
   cursor.execute(...)
   cursor.execute(...)
   ```
   for Presto it wouldn't poll to check that the first statement had finished before executing the second. It seems that some DB-API's have the `nextset` method (though this isn't universal) but reading through code snippets it seems the best way to ensure that multi-statements execute sequentially for all engine types is to simply call `fetchall` from the cursor which waits until the statement is done, i.e., [here's](https://github.com/dropbox/PyHive/blob/master/pyhive/common.py#L105) the logic for Presto.
   
   Note that when using the `sqlalchemy.engine.base.Connection` (without a cursor) the following would work (though I'm not sure why):
   ```
   conn = engine.connect()
   conn.execute(...)
   conn.execute(...)
   ```
   However this approach isn't via use the cursor to execute queries via `db_engine_spec.execute`. 

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