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This example illustrates how the NOW and TODAY functions operate. Both functions generate outputs of Datetime data type.

NOW - Generates valid Datetime values for the current timestamp in the specified time zone. See NOW Function.
TODAY - Generates valid Datetime for the current date in the specified time zone. See TODAY Function.
DATEDIF - Calculates the difference between two Datetime values based on a specific unit of measure. See DATEDIF Function.

Source:

The following table includes flight arrival information for Los Angeles International airport.

FlightNumber	Gate	Arrival
1234	1	2/15/17 11:35
212	2	2/15/17 11:58
510	3	2/15/17 11:21
8401	4	2/15/17 12:08
99	5	2/16/17 12:12
116	6	2/16/17 13:32
876	7	2/15/17 16:43
9494	8	2/15/17 21:00
102	9	2/14/17 19:21
77	10	2/16/17 12:31

Transformation:

You are interested in generating a status report on today's flights. To assist, you must generate columns with the current date and time values:

Tip: You should create separate columns containing static values for NOW and TODAY functions. Avoid creating multiple instances of each function in your dataset, as the values calculated in them can vary at execution time.

Next, you want to identify the flights that are landing today. In this case, you can use the DATEDIF function to determine if the Arrival value matches the currentTime value within one day:

NOTE: The DATEDIF function computes difference based on the difference from the first date to the second date based on the unit of measure. So, a timestamp that is 23 hours difference from the base timestamp can be within the same unit of day, even though the dates may be different (2/15/2017 vs. 2/14/2017).

Since you are focusing on today only, you can remove all of the rows that do not apply to today:

Now focusing on today's dates, you can calculate the difference between the current time and the arrival time by the minute:

Using the numeric values in the status column, you can compose the following transform, which identifies status of each flight:

Results:

You now have a daily flight status report:

currentDate	currentTime	FlightNumber	Gate	Arrival	status
2017-02-15	2017-02-15·11:46:12	1234	1	2/15/17 11:35	landed
2017-02-15	2017-02-15·11:46:12	212	2	2/15/17 11:58	arriving
2017-02-15	2017-02-15·11:46:12	510	3	2/15/17 11:21	arrived
2017-02-15	2017-02-15·11:46:12	8401	4	2/15/17 12:08	scheduled
2017-02-15	2017-02-15·11:46:12	876	7	2/15/17 16:43	scheduled
2017-02-15	2017-02-15·11:46:12	9494	8	2/15/17 21:00	scheduled
2017-02-15	2017-02-15·11:46:12	102	9	2/14/17 19:21	arrived

The currentDate, currentTime, and today columns can be deleted.