Optimize the view metrics_per_day adding an index

Author: sfauvel

mithril-aggregator/src/event_store/database/migration.rs

@@ -23,13 +23,14 @@ create table if not exists event (
         SqlMigration::new(
             2,
             r#"
-create view if not exists metrics_per_day as select date(metric_date) as date, action as counter_name, sum(counter) value from 
+create view if not exists metrics_per_day as select metric_date as date, action as counter_name, sum(counter) value from 
     (
-        select action, json_extract(content, '$.content.counter') counter, json_extract(content, '$.content.date') metric_date 
+        select action, json_extract(content, '$.content.counter') counter, date(json_extract(content, '$.content.date')) metric_date 
         from event 
         where source='Metrics'
     ) 
 group by action, date;
+create index metric_date_index on event(date(json_extract(content, '$.content.date')));
             "#,
         ),
     ]