I store the employees' vacations in an SQL table as 2 columns of dates (StartDate : EndDate) along with the vacation type. I can't figure out the best approach to check for some rules, every time an employee tries to request a new vacation on the system:

  1. An employee can't connect two vacations unless he/she shows up to work in between.
  2. An employee can connect vacations but with a specific type.

What I tried to do is create a temp calendar table of the full-year dates, and joined the dates of the vacations like this:

Dates DutyState Vacation Type
2023-01-01 Work True A
2023-01-02 Work True A
2023-01-03 Work False NULL
2023-01-04 OFF False NULL
2023-01-05 OFF False NULL
2023-01-06 Work False NULL
2023-01-07 Work False NULL
2023-01-08 Work True B
2023-01-09 OFF False NULL
2023-01-10 OFF False NULL
2023-01-11 Work False NULL

To clarify the rules more:

This employee has a type A vacation from 1 to 2 Jan, then he has another one on 8 Jan of type B, He can request a vacation of any type other than A & B in any other work day(s) in this table (only these 2 types has restrictions), and also can request a vacation of types A or B only on 6 Jan. Only workdays break the connection rule, that's why he can't request type A or B on 11 Jan (Because only Off days in between it and the previous vacation on 8 Jan) also he can't request A or B on 3 Jan (another vacation on 2 Jan connect to it). But he can request type C on any day. How to check for that in SQL?

NOTE: Workdays/Off count may vary. It's not always 3/2, and it's not related to Weekdays or Weekends.

1 Answer 1


It's okay, I figured it out: I eliminated the OFF days and then used a combination of LAG/LEAD in a case statement like this:

        WHEN DATEDIFF(DAY, LAG(Dates, 1) OVER(ORDER BY Dates ASC), Dates) = 1 
            AND LAG(vacID, 1) OVER(ORDER BY Dates ASC) <> vacID 
            AND LAG([Type], 1) OVER(ORDER BY Dates ASC) IN (A, B) 
            AND [Type] IN (A, B) 
            THEN 1 
        WHEN DATEDIFF(DAY, LEAD(Dates, 1) OVER(ORDER BY Dates ASC), Dates) = 1 
            AND LEAD(vacID, 1) OVER(ORDER BY Dates ASC) <> vacID 
            AND LEAD([Type], 1) OVER(ORDER BY Dates ASC) IN (A, B) 
            AND [Type] IN (A, B) 
            THEN 1 
        ELSE 0 
    END AS connects  
    FROM #DT_CalVac WHERE DutyState <> 'OFF';

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