[MySQL] grouping
\n\nSELECT \n    event_day AS day, \n    emp_id, \n    SUM(out_time - in_time) AS total_time\nFROM Employees\nGROUP BY 1, 2\n
\n```\nSELECT \n    event_day AS day, \n    emp_id, \n    SUM(out_time - in_time) AS total_time\nFROM Employees\nGROUP BY 1, 2\n```
['MySQL']