**For '+' operator: **

- If you add a decimal value to a timestamp, the result depends on the session/system parameter
`TIMESTAMP_ARTITHMETIC_BEHAVIOUR`:- When
`TIMESTAMP_ARTITHMETIC_BEHAVIOUR`=`'INTERVAL'`- the decimal is rounded to an integer, and a certain number of full days are added(this is similar to function ADD_DAYS).

- When
`TIMESTAMP_ARTITHMETIC_BEHAVIOUR`=`'DOUBLE'`- the fraction of days are added (hours, minutes, ...).

- When
- When adding the number of years or months (for example,
`INTERVAL '3' MONTH`) on a date whose day is the last day of the month, then the last day of the resulting month is returned ( similar to ADD_MONTHS).

**For '-' operator**

- The difference between two datetime values depends on the session/system parameter
`TIMESTAMP_ARITHMETIC_BEHAVIOR`:`TIMESTAMP_ARITHMETIC_BEHAVIOR`=`'INTERVAL'`- the result is an interval (similar to function DAYS_BETWEEN).`TIMESTAMP_ARITHMETIC_BEHAVIOR`=`'DOUBLE'`- the result is a double.

- The difference of a date and a decimal is similar to the + operator with a negative value, thus subtracting days instead of adding them.
- The difference between two interval values return an interval.
- When subtracting the number of years or months (for example,
`INTERVAL '3' MONTH`) on a date whose day is the last day of the month, then the last day of the resulting month is returned (similar to ADD_YEARS and ADD_MONTHS).