DATEDIFF()
Difference between two datetime values in a datetime unit
BIGINT, or NUMERIC(18,1) for MILLISECOND
DATEDIFF (<args>)
<args> ::=
    <unit> FROM <moment1> TO <moment2>
  | <unit>, <moment1>, <moment2>
<unit> ::=
    YEAR | MONTH | WEEK | DAY
  | HOUR | MINUTE | SECOND | MILLISECOND
<momentN> ::= a DATE, TIME or TIMESTAMP expression
| Parameter | Description | 
|---|---|
| unit | Date/time unit | 
| moment1 | An expression of the  | 
| moment2 | An expression of the  | 
Returns the number of years, months, weeks, days, hours, minutes, seconds or milliseconds elapsed between two date/time values.
- 
DATEandTIMESTAMParguments can be combined.No other mixes are allowed.
- 
With TIMESTAMPandDATEarguments, all units can be used.
- 
With TIMEarguments, onlyHOUR,MINUTE,SECONDandMILLISECONDcan be used.
- 
DATEDIFFdoesn’t look at any smaller units than the one specified in the first argument.As a result,- 
datediff (year, date '1-Jan-2009', date '31-Dec-2009')returns 0, but
- 
datediff (year, date '31-Dec-2009', date '1-Jan-2010')returns 1
 
- 
- 
It does, however, look at all the bigger units. So: - 
datediff (day, date '26-Jun-1908', date '11-Sep-1973')returns 23818
 
- 
- 
A negative result value indicates that moment2 lies before moment1.