Date Math Gotcha
We can sometimes get unexpected results, and this applies to several different programming languages and Query Date Math.
A month can contain 28 29 30 or 31 days.
A year can contain 365 or 366 days.
- Start with date 2005-03-31
- add one month
- this gets date 2005-04-30
- subtract one month
- this gets date 2005-03-30
In this example we learn that if the math would produce an invalid date 2005-04-31, it lowers the result to the previous valid date, but there is no "memory" of this "rounding".
- subtract 2005-03-31
- from 2005-04-30
- the result is ZERO months
- because it sees that 30 is less than 31 and not recognize that these are last days of months