The EXTRACT function extracts a portion of a DateTime, such as the day of the week or month of the year.

This is useful in situations where the data must be filtered or grouped by a slice of its timestamps, for example computing the total sales that occurred on any Monday.

<ExtractExpr>   ::=  EXTRACT(<expr>,<DateTimeUnit>)
<DateTimeUnit>  ::=  SECOND | MINUTE | HOUR | DAY_OF_WEEK |
                     DAY_OF_MONTH | DAY_OF_YEAR | DATE | WEEK |
                     MONTH | QUARTER | YEAR

For example, given a DateTime property "TimeStamp" with a value representing 10/13/2009 11:35:12.000, the EXTRACT operator could be used to compute the following results:

EXTRACT("TimeStamp", SECOND)       = 12
EXTRACT("TimeStamp", MINUTE)       = 35
EXTRACT("TimeStamp", HOUR)         = 11
EXTRACT("TimeStamp", DATE)         = 13
EXTRACT("TimeStamp", WEEK)         = 40   /* Zero-indexed */
EXTRACT("TimeStamp", MONTH)        = 10
EXTRACT("TimeStamp", QUARTER)      = 3    /* Zero-indexed */
EXTRACT("TimeStamp", YEAR)         = 2009
EXTRACT("TimeStamp", DAY_OF_WEEK)  = 4    /* Zero-indexed */
EXTRACT("TimeStamp", DAY_OF_MONTH) = 13
EXTRACT("TimeStamp", DAY_OF_YEAR)  = 286  /* Zero-indexed */

As a simple example of using this functionality, the following query groups transaction records containing TimeStamp and Amount properties by quarter, and for each quarter computes the total sales that occurred on a Monday (DAY_OF_WEEK=1):

RETURN Quarters AS
SELECT SUM(Amount) AS Total
       TRUNC(TimeStamp, QUARTER) AS Qtr
WHERE EXTRACT(TimeStamp,DAY_OF_WEEK) = 1
GROUP BY Qtr