TIMESTAMPDIFF

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. The value specifies the interval that is used to determine the difference between two timestamps. Valid values of the interval follow.

Table 1. Valid values for numeric-expression and equivalent intervals that are used to determine the difference between two timestamps
Valid values for numeric-expression	Equivalent intervals
1	Microseconds
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. If the string-expression has more than 6 digits to the right of the decimal point, the string will be truncated to 6 digits. The argument must be an expression that returns a value of a built-in character string or a graphic string.

If a positive or negative sign is present, it is the first character of the string. The following table describes the elements of the character string duration:

Table 2. TIMESTAMPDIFF String Elements
String elements	Valid values	Character position from the decimal point (negative is left)
Years	1-9998 or blank	-14 to -11
Months	0-11 or blank	-10 to -9
Days	0-30 or blank	-8 to -7
Hours	0-24 or blank	-6 to -5
Minutes	0-59 or blank	-4 to -3
Seconds	0-59	-2 to -1
Decimal separator	period	0
Microseconds	000000-999999	1 to 6

The result of the function is an integer with the same sign as string-expression. If either argument can be null, the result can be null; if either argument is null, the result is the null value.

The returned value is determined for each interval as indicated by the following table:

Table 3. TIMESTAMPDIFF Computations
Result interval	Computation using duration elements
Years	years
Quarters	integer value of (months+(years*12))/3
Months	months + (years*12)
Weeks	integer value of ((days+(months30))/7)+(years52)
Days	days + (months30)+(years365)
Hours	hours + ((days+(months30)+(years365))*24)
Minutes (the absolute value of the duration must not exceed 40850913020759.999999)	minutes + (hours+((days+(months30)+(years365))24))60
Seconds (the absolute value of the duration must be less than 680105031408.000000)	seconds + (minutes+(hours+((days+(months30)+(years365))24))60 )*60
Microseconds (the absolute value of the duration must be less than 3547.483648)	microseconds + (seconds+(minutes60))1000000

The following assumptions are used when converting the element values to the requested interval type:

One year has 365 days.
One year has 52 weeks.
One year has 12 months.
One quarter has 3 months.
One month has 30 days.
One week has 7 days.
One day has 24 hours.
One hour has 60 minutes.
One minute has 60 seconds.
One second has 1000000 microseconds.

The use of these assumptions imply that some result values are an estimate of the interval. Consider the following examples:

Difference of 1 month where the month has less than 30 days.
```
TIMESTAMPDIFF(16, CHAR(TIMESTAMP('1997-03-01-00.00.00') - TIMESTAMP('1997-02-01-00.00.00') ) )
```
The result of the timestamp arithmetic is a duration of 00000100000000.000000, or 1 month. When the TIMESTAMPDIFF function is invoked with 16 for the interval argument (days), the assumption of 30 days in a month is applied and the result is 30.
Difference of 1 day less than 1 month where the month has less than 30 days.
```
TIMESTAMPDIFF(16, CHAR(TIMESTAMP('1997-03-01-00.00.00') - TIMESTAMP('1997-02-02-00.00.00') ) )
```
The result of the timestamp arithmetic is a duration of 00000027000000.000000, or 27 days. When the TIMESTAMPDIFF function is invoked with 16 for the interval argument (days), the result is 27.
Difference of 1 day less than 1 month where the month has 31 days.
```
TIMESTAMPDIFF(64, CHAR(TIMESTAMP('1997-09-01-00.00.00') - TIMESTAMP('1997-08-02-00.00.00') ) )
```
The result of the timestamp arithmetic is a duration of 00000030000000.000000, or 30 days. When the TIMESTAMPDIFF function is invoked with 64 for the interval argument (months), the result is 0. The days portion of the duration is 30, but it is ignored because the interval specified months.

Example

The following statement estimates the age of employees in months and returns that value as AGE_IN_MONTHS:

SELECT 
    TIMESTAMPDIFF(64,
    CAST(CURRENT_TIMESTAMP-CAST(BIRTHDATE AS TIMESTAMP) AS CHAR(22))) 
      AS AGE_IN_MONTHS
  FROM EMPLOYEE