MEMORY EFFICIENT SOL QUERY | SIMPLE
GROUPING SAME ENTITY AND ADDING THEIR COLUMN VALUES\n\n\nSELECT  event_day AS day,emp_id,SUM(out_time - in_time) AS total_time FROM EMPLOYEES GROUP BY event_day
**GROUPING SAME ENTITY AND ADDING THEIR COLUMN VALUES**\n```\n\nSELECT  event_day AS day,emp_id,SUM(out_time - in_time) AS total_time FROM EMPLOYEES GROUP BY event_day,emp_id;\n\n```
['MySQL']