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Using a Custom Time Dimension in a Logical Data Model

In some situations, you need to slice your data by timestamps. For example:

To predict the number of call center personnel required at different times of a day, you may want to see data from a call center sliced by hour and minute or by hour and quarter hour (15-minute intervals).
To plan the movie schedule at a cinema, you may need to know how many tickets are sold for particular movies at different times of day across a selected range of dates.

To handle such situations, we recommend that you split the date and time into separate attributes. To do so:

Create a date dimension for the date attribute using either a standard (default) calendar, or a custom fiscal calendar.
Add a custom time dimension to handle the time of day.

You can use the custom time dimension together with a GoodData date dimension for slicing the data, or you can use it independently if you need to see trends by time-of-day across dates.

We recommend that you not create a timestamp dimension because of the large amount of data required. For example, a day consists of 1,440 minutes or 86,400 seconds. A timestamp to the minute for the years 1900 through 2050 would contain 79.4 million rows. A timestamp to the second would contain 4.8 billion rows. Besides, you cannot use date filters and attributes for day, week, quarter, and year with a timestamp dimension.

A custom time dimension, on the other hand, covers a 24-hour period with one row per desired time interval, such as:

Hour and minute
Hour, minute, and second

When you are creating a custom time dimension, consider the following:

Adding attributes for any custom intervals (for example, quarter hour)
Adding labels for any custom display formats (for example, 12-hour clock vs. 24-hour clock)
Adding labels for sorting so that hours, minutes, and seconds are displayed without leading zeros, and so that AM times precede PM times when using a 12-hour clock

Custom Time Dimensions in a Logical Data Model

The following picture shows a sample logical data model (LDM) for collecting data from a call center. The LDM has two custom time dimension datasets: Started Time and Ended Time.

The following picture shows the attributes and labels in the Started Time time dimension dataset:

Load the Data into Your Data Warehouse

Follow these steps to create and load Data Warehouse tables for your custom time dimension:

Create a table (wh_time_of_day) in your Data Warehouse instance using the TIME data type.

DROP TABLE IF EXISTS wh_time_of_day;
CREATE TABLE wh_time_of_day
  (time_of_day        TIME)
   SEGMENTED BY HASH(0) ALL NODES
;

Generate 24 hours of data:

Create a temporary table (tmp_hour) for hours with 24 rows containing a single column that holds values of ‘00’ through ‘23’.

CREATE LOCAL TEMPORARY TABLE tmp_hour 
  (hour_of_day     CHAR(2) )
 ON COMMIT PRESERVE ROWS;
         
INSERT INTO tmp_hour VALUES('00');
...
INSERT INTO tmp_hour VALUES('23');

Create a temporary table (tmp_min_sec) for minutes and seconds with 60 rows containing a single column that holds values of ‘00’ through ‘59’.

CREATE LOCAL TEMPORARY TABLE tmp_min_sec 
  (min_sec_of_day  CHAR(2) )
 ON COMMIT PRESERVE ROWS;
INSERT INTO tmp_min_sec VALUES('00'); 
...
INSERT INTO tmp_min_sec VALUES('59');

Load the data to the Data Warehouse table (wh_time_of_day). In this example, you are going to truncate and load the wh_time_of_day table using INSERT with a SELECT of all rows from tmp_hour with a Cartesian join (CROSS JOIN) to tmp_min_sec for minutes. The Cartesian join will join each hour (00-23) with minutes (00-59). If the time dimension needs to be down to the second, add another Cartesian join that will join each hour and minute to each second (00-59).
```
TRUNCATE TABLE wh_time_of_day;
INSERT /*+direct*/ INTO wh_time_of_day
  SELECT TO_TIMESTAMP(a.hour_of_day || ':' || b.min_sec_of_day || ':' ||
         c.min_sec_of_day, 'HH:MI:SS')
    FROM tmp_hour a
      CROSS JOIN tmp_min_sec b
      CROSS JOIN tmp_min_sec c 
   ORDER BY a.hour_of_day, b.min_sec_of_day, c.min_sec_of_day; 
```

Load the output stage table (or GoodData dataset) from the Data Warehouse table (wh_time_of_day), using SQL for formatting the desired attributes and labels. The following are some examples of formatting the various attributes and labels:

-- SELECT from wh_time_of_day...
-- 24 hour clock time formats
TO_CHAR(time_of_day, 'HH:MI:SS') AS time_hhmmss,
TO_CHAR(time_of_day, 'HH:MI') AS time_hhmm,
TO_CHAR(time_of_day, 'HH') AS time_hh,
-- 12 hour clock time in hours
CASE
   WHEN LEFT(TO_CHAR(time_of_day, 'HH12'), 1) = '0'
        THEN RIGHT(TO_CHAR(time_of_day, 'HH12 AM'), 4)
   ELSE TO_CHAR(time_of_day, 'HH12 AM')
   END
  AS time_hour,
EXTRACT(HOUR FROM time_of_day) AS time_hour_sort, -- integer for hour sort

-- 12 hour clock down to minutes
CASE
   WHEN LEFT(TO_CHAR(time_of_day, 'HH12'), 1) = '0'
        THEN RIGHT(TO_CHAR(time_of_day, 'HH12:MI AM'), 7)
   ELSE TO_CHAR(time_of_day, 'HH12:MI AM')
   END
  AS time_minute,
(EXTRACT(HOUR FROM time_of_day) * 100) + EXTRACT(MINUTE FROM time_of_day) 
      AS time_minute_sort,  -- integer HHMM for sorting

-- 12 hour clock down to seconds
CASE
   WHEN LEFT(TO_CHAR(time_of_day, 'HH12'), 1) = '0'
        THEN RIGHT(TO_CHAR(time_of_day, 'HH12:MI:SS AM'), 10)
   ELSE TO_CHAR(time_of_day, 'HH12:MI:SS AM')
   END  
  AS time_second,
(EXTRACT(HOUR FROM time_of_day) * 10000) + 
(EXTRACT(MINUTE FROM time_of_day) * 100) +
 CAST(TO_CHAR(time_of_day, 'SS') AS INTEGER) 
  AS time_second_sort,  -- integer HHMMSS for sorting

-- half hour intervals (similar for quarter hour intervals)
CASE  
   WHEN EXTRACT(MINUTE FROM time_of_day) < 30
    AND LEFT(TO_CHAR(time_of_day, 'HH12'), 1) = '0'
        THEN RIGHT(TO_CHAR(time_of_day, 'HH12'), 1) || ':00 ' ||  
             TO_CHAR(time_of_day, 'AM')
   WHEN EXTRACT(MINUTE FROM time_of_day) < 30
        THEN TO_CHAR(time_of_day, 'HH12') || ':00 ' || 
             TO_CHAR(time_of_day, 'AM')
   WHEN EXTRACT(MINUTE FROM time_of_day) < 60
    AND LEFT(TO_CHAR(time_of_day, 'HH12'), 1) = '0'
        THEN RIGHT(TO_CHAR(time_of_day, 'HH12'), 1) || ':30 ' || 
                   TO_CHAR(time_of_day, 'AM')
   ELSE TO_CHAR(time_of_day, 'HH12') || ':30 ' || TO_CHAR(time_of_day, 'AM')
  END     
 AS time_halfhour,
-- half hour interval sort (integer formatted as HH00 or HH30)
CASE
   WHEN EXTRACT(MINUTE FROM time_of_day) < 30
        THEN (EXTRACT(HOUR FROM time_of_day) * 100) 
   ELSE (EXTRACT(HOUR FROM time_of_day) * 100) + 30
   END
  AS time_halfhour_sort

Import and Export a Logical Data Model

Create the Output Stage based on Your Logical Data Model