override get_view_names in PrestoEngineSpec

[youngyjd]

When fetching metadata for presto engine spec we got an error which says:

ts=2018-11-28T20:42:52.414Z uuid=98709625-59fd-4d9d-88e2-22471db6fec0 app=superset name=root lvlname=ERROR lvlno=40 pid=103884 request_id=3b7d72c3-4949-97a7-9749-92da9cd4e2a9 exc="Traceback (most recent call last):
File \"/srv/venvs/service/trusty/service_venv_python3.6/lib/python3.6/site-packages/superset/models/core.py\", line 947, in all_view_names_in_schema
inspector=self.inspector, schema=schema)
File \"/srv/venvs/service/trusty/service_venv_python3.6/lib/python3.6/site-packages/superset/db_engine_specs.py\", line 306, in get_view_names
return sorted(inspector.get_view_names(schema))
File \"/srv/venvs/service/trusty/service_venv_python3.6/lib/python3.6/site-packages/sqlalchemy/engine/reflection.py\", line 324, in get_view_names 
info_cache=self.info_cache)
File \"/srv/venvs/service/trusty/service_venv_python3.6/lib/python3.6/site-packages/sqlalchemy/engine/interfaces.py\", line 330, in get_view_names
raise NotImplementedError()
NotImplementedError" msg=

Then I found get_view_names() is not implemented in https://github.com/dropbox/PyHive/blob/e25fc8440a0686bbb7a5db5de7cb1a77bdb4167a/pyhive/sqlalchemy_presto.py because get_table_names() function returns all table names and view names.

For Hive, I observed that every time when superset tries to fetch table list and view list in default schema, it issues SHOW TABLES IN default twice. I found out that's because get_view_names() is indeed a call of get_table_names. Since HiveEngineSpec() inherits from PrestoEngineSpec(), we can just leverage the get_view_names() in PrestoEngineSpec().

[codecov-io]

Codecov Report

Merging #6459 into master will decrease coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff            @@
##           master   #6459      +/-   ##
=========================================
- Coverage   73.31%   73.3%   -0.01%     
=========================================
  Files          67      67              
  Lines        9589    9591       +2     
=========================================
+ Hits         7030    7031       +1     
- Misses       2559    2560       +1

Impacted Files	Coverage Δ
superset/db_engine_specs.py	55.02% <50%> (-0.02%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4579b12...bd3ffa6. Read the comment docs.

[youngyjd]

@betodealmeida

[betodealmeida]

Looks good! Note that it should be trivial to implement get_view_names in the Presto dialect; all you need to do is run this query:

SELECT table_name FROM information_schema.views WHERE table_schema='{schema}'

Might be worth doing a PR for PyHive. ;)