MySQL - 96% Faster using Group By and Sum
```\n# Write your MySQL query statement below\nselect \nevent_day as day,\nemp_id,\nsum(out_time-in_time) as total_time\n\nfrom\nemployees \n\ngroup by emp_id, 
```\n# Write your MySQL query statement below\nselect \nevent_day as day,\nemp_id,\nsum(out_time-in_time) as total_time\n\nfrom\nemployees \n\ngroup by emp_id, event_day
['MySQL']