Week beginning Monday time grain for MySQL (#2014)

diff --git a/superset/db_engine_specs.py b/superset/db_engine_specs.py
index 80cc618..8bcb1a3 100644
--- a/superset/db_engine_specs.py
+++ b/superset/db_engine_specs.py
@@ -139,6 +139,9 @@
               "+ INTERVAL QUARTER({col}) QUARTER - INTERVAL 1 QUARTER"),
         Grain("year", _('year'), "DATE(DATE_SUB({col}, "
               "INTERVAL DAYOFYEAR({col}) - 1 DAY))"),
+        Grain("week_start_monday", _('week_start_monday'),
+              "DATE(DATE_SUB({col}, "
+              "INTERVAL DAYOFWEEK(DATE_SUB({col}, INTERVAL 1 DAY)) - 1 DAY))"),
     )
 
     @classmethod