Time Difference

Since you say that the columns contain both data and time, I'll assume they're using the datatype TIMESTAMP.

In that case, use the TIMESTAMPDIFF function.

Here's the defininition / documentation of that function.

HTH,
DaveSlash

The TIMESTAMPDIFF function returns an estimated number of intervals of the type defined by the first argument, based on the difference between two timestamps. numeric-expression The first argument must be a built-in data type of either INTEGER or SMALLINT. Valid values of interval (the first argument) are:
 
1 - Fractions of a second
2 - Seconds
4 - Minutes
8 - Hours
16 - Days
32 - Weeks
64 - Months
128 - Quarters
256 - Years 
 
string-expression
 string-expression is the result of subtracting two timestamps and converting the result to a string of length 22. The argument must be an expression that returns a value of a built-in character string or a graphic string. If string-expression is a character or graphic string, it must not be a CLOB or DBCLOB. 
 
The result of the function is an integer. If either argument can be null, the result can be null; if either argument is null, the result is the null value. 
 
The following assumptions may be used in estimating the difference: 
- there are 365 days in a year 
- there are 30 days in a month 
- there are 24 hours in a day 
- there are 60 minutes in an hour 
- there are 60 seconds in a minute
 
These assumptions are used when converting the information in the second argument, which is a timestamp duration, to the interval type specified in the first argument. The returned estimate may vary by a number of days. For example, if the number of days (interval 16) is requested for a difference in timestamps for '1997-03-01-00.00.00' and '1997-02-01-00.00.00', the result is 30. This is because the difference between the timestamps is 1 month so the assumption of 30 days in a month applies. 
 
Example - Estimate the age of employees in months.
 
SELECT
   TIMESTAMPDIFF(64,
    CAST(CURRENT_TIMESTAMP-CAST(BIRTHDATE AS TIMESTAMP) AS CHAR(22))) 
      AS AGE_IN_MONTHS 
FROM EMPLOYEE

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