LeetCode MySQL-1741. Find Total Time Spent by Each Employee

    AllenLi
    LeetCode MySQL

    Write an SQL query to calculate the total time in minutes spent by each employee on each day at the office. Note that within one day, an employee can enter and leave more than once. The time spent in the office for a single entry is out_time – in_time.
    Return the result table in any order.

    寫一個 SQL Query來計算每個員工每天在辦公室所花費的總時間(以分鐘為單位)，
員工可以進入或離開超過一次，且花費時間為 out_time - in_time。
可任意排序結果。

    Table: Employees

    +-------------+------+
| Column Name | Type |
+-------------+------+
| emp_id      | int  |
| event_day   | date |
| in_time     | int  |
| out_time    | int  |
+-------------+------+
(emp_id, event_day, in_time) is the primary key of this table.
The table shows the employees' entries and exits in an office.
event_day is the day at which this event happened, in_time is the minute at which the employee entered the office, and out_time is the minute at which they left the office.
in_time and out_time are between 1 and 1440.
It is guaranteed that no two events on the same day intersect in time, and in_time < out_time.

    Example 1:

    Input: 
Employees table:
+--------+------------+---------+----------+
| emp_id | event_day  | in_time | out_time |
+--------+------------+---------+----------+
| 1      | 2020-11-28 | 4       | 32       |
| 1      | 2020-11-28 | 55      | 200      |
| 1      | 2020-12-03 | 1       | 42       |
| 2      | 2020-11-28 | 3       | 33       |
| 2      | 2020-12-09 | 47      | 74       |
+--------+------------+---------+----------+
Output: 
+------------+--------+------------+
| day        | emp_id | total_time |
+------------+--------+------------+
| 2020-11-28 | 1      | 173        |
| 2020-11-28 | 2      | 30         |
| 2020-12-03 | 1      | 41         |
| 2020-12-09 | 2      | 27         |
+------------+--------+------------+
Explanation: 
Employee 1 has three events: two on day 2020-11-28 with a total of (32 - 4) + (200 - 55) = 173, and one on day 2020-12-03 with a total of (42 - 1) = 41.
Employee 2 has two events: one on day 2020-11-28 with a total of (33 - 3) = 30, and one on day 2020-12-09 with a total of (74 - 47) = 27.

    Solution:
    1. 選擇標題 event_day 為 day。
    2. 選擇標題 emp_id。
    3. 選擇標題 total_time 為 (out_time - in_time)。
    4. 來自 Employees 的 table。
    5. 以 event_day 與 emp_id 為群組。
    6. 以 event_day 做排序。

    Code1:

    SELECT event_day AS day,
	emp_id,
    SUM(out_time - in_time) AS total_time
    FROM Employees
GROUP BY event_day, emp_id
ORDER BY event_day;

    newEmployees

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