MySQL: A query to work with timetables?

Question

In the project I'm working on right now the system stores employees' timetables in the table with the following structure:

employee_id | mon_h_s | mon_m_s | mon_h_e | mon_s_e | tue_h_s | tue_m_s | etc.
------------------------------------------------------------------------------
      1         06         00        14        30        06        00     ...
      2         18         30        07        00        21        00     ...

where:

mon_h_s - monday hours start

mon_m_s - monday minutes start

mon_h_e - monday hours end

mon_m_e - monday minutes end

tue_... - tuesday...

Every day of the week has 4 fields: hours start, minutes start, hours end, minutes end.

So, from the table above we can see that:

• employee with the id 1 works from 06:00 to 14:30 on Monday

• employee with the id 2 works from 18:30 to 07:00 on Monday (basically, between Monday and Tuesday, at night)

The problem is that I'm not sure how to create a SQL query which takes into account everything including time overlapping (at night time). For example, we need to find an employee who works at 6am (06:00) on Tuesday. In our case both employees (id 1 and id 2) would satisfy this criteria. Employee with the id 1 starts his work at 06:00 on Tuesday, and employee with the id 2 works until 07:00 Tuesday (starts on Monday though).

Any suggestions on how to solve this problem would be greatly appreciated.

Answer 1

Probably something like:

SELECT (1440 + ((mon_h_e*60)+mon_m_e) - ((mon_h_e*60)+mon_m_e)) % 1440

This will give you the time worked in minutes. Basically, it adds 1440 (minutes in a day, or 24h*60min/h) to the difference between end time and start time, and keep the rest (modulo) of 1440.

Now for the design part:

If you can, redesign your table. Your table need not have all days of the week in one row, that will make tallying of weekly times very tedious.

You should consider using real datetimes.

employee_id | entrytime           | exittime
          1 | 2011-10-31 06:00:00 | 2011-10-31 14:30:00
          1 | 2011-11-01 06:00:00 | null
          2 | 2011-10-31 18:30:00 | 2011-11-01 07:00:00
          2 | 2011-11-01 21:00:00 | null

That way, you have:

1. Full access to all date and time functions in MySQL
2. Easy calculation of duration
3. Easy filtering on incomplete periods

Answer 2

There are four basic cases that you need o handle

A -> when time of lecture starts before given time
B -> when time of lecture starts after given time but falls within range of ending time
C -> when time of lecture starts within given time but ends after
D -> when time of lecture starts before given time and ends after given time

Now, this can be accomplished using simple OR conditions