Need help in finding nearest shift time in SQL

I have following table for shifts.

AutoId StartTime       EndTime
1      08:00:00 AM     0开发者_如何学Python4:00:00 PM
2      04:00:00 PM     12:00:00 AM
3      12:00:00 AM     08:00:00 AM

Now I want to assign Shifts to employees automatically..

For example, if someone comes 7:32 AM then his shift should be the first shift, that is, from 08:00:00 AM to 4:00:00 PM. If someone comes 11:45 PM then it should be automatically set as the third shift.

I also want that if an employee come in during the first hour of the shift then it should also work.

How do I find the nearest shift by giving employee InTime?

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Something like:

SELECT AutoId, StartTime, EndTime
  FROM Shifts
 WHERE StartTime = (SELECT MIN(StartTime) FROM Shifts WHERE DATEADD(hh, 1, StartTime) > inTime)

EDIT: Added grace period