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Calculate time between related records

Question asked by RobertGardner on May 9, 2011
Latest reply on May 10, 2011 by RestaurantCharlie


Calculate time between related records


I have a Tests table with 3 fields:

  1. TestDate
  2. Test (specifies which test taken)
  3. Student

A particular student may take multiple different tests, and I need to calculate the time between their most recent test and the one prior.  I've been trying the GetNthRecord function, but I can't figure out 2 things:

  1. I can pull the date from the previous record, but I cannot figure out how to write the calculation so that it returns the correct number.  (For instance, if the previous test was on the same date, it should return a zero.  It does not)
  2. The previous record is not always for the same student, and I want to calculate the difference in time between records of the same student.

Any help would be appreciated.