Fixed Time Grain and Added Drill to README (#7635)

* Fixed Time Grain and Added Drill to README

* Capitalization Fix

README.md

@@ -112,6 +112,7 @@ Superset can be used to visualize data out of most databases:
 * Redshift
 * Clickhouse
 * Apache Kylin
+* Apache Drill
 * Google BigQuery
 * **more!** look for the availability of a SQLAlchemy dialect for your database
   to find out whether it will work with Superset

superset/db_engine_specs.py

@@ -753,16 +753,16 @@ class DrillEngineSpec(BaseEngineSpec):
 
     time_grain_functions = {
         None: '{col}',
-        'PT1S': "nearestDate({col}, 'SECOND')",
-        'PT1M': "nearestDate({col}, 'MINUTE')",
-        'PT15M': "nearestDate({col}, 'QUARTER_HOUR')",
-        'PT0.5H': "nearestDate({col}, 'HALF_HOUR')",
-        'PT1H': "nearestDate({col}, 'HOUR')",
-        'P1D': 'TO_DATE({col})',
-        'P1W': "nearestDate({col}, 'WEEK_SUNDAY')",
-        'P1M': "nearestDate({col}, 'MONTH')",
-        'P0.25Y': "nearestDate({col}, 'QUARTER')",
-        'P1Y': "nearestDate({col}, 'YEAR')",
+        'PT1S': "NEARESTDATE({col}, 'SECOND')",
+        'PT1M': "NEARESTDATE({col}, 'MINUTE')",
+        'PT15M': "NEARESTDATE({col}, 'QUARTER_HOUR')",
+        'PT0.5H': "NEARESTDATE({col}, 'HALF_HOUR')",
+        'PT1H': "NEARESTDATE({col}, 'HOUR')",
+        'P1D': "NEARESTDATE({col}, 'DAY')",
+        'P1W': "NEARESTDATE({col}, 'WEEK_SUNDAY')",
+        'P1M': "NEARESTDATE({col}, 'MONTH')",
+        'P0.25Y': "NEARESTDATE({col}, 'QUARTER')",
+        'P1Y': "NEARESTDATE({col}, 'YEAR')",
     }
 
     # Returns a function to convert a Unix timestamp in milliseconds to a date