如何在TIMESTAMP列中找到时间或范围

Question

I have a list of events with begin and end timestamps in GMT UTC+0. The column is type DATE but has time as well (not designed by me).

The begin timestamp is plainly indexed

I need to find events the occur between, say, 06:00 and 22:00 Localtime which is Eastern Daylight Time UTC-4. on any day between March 31th and April 2nd.

The Only way I've found to do it is convert it TO_CHAR() then. It's also not using the index because it's using TO_CHAR function.

Here's what I go so far.

  TO_CHAR(e.begin_time,'HH24:MI') >= TO_CHAR(FROM_TZ(TO_TIMESTAMP('06:00','HH24:MI'),'US/Eastern') AT TIME ZONE '+00:00','HH24:MI') AND 
  TO_CHAR(e.begin_time,'HH24:MI') <= TO_CHAR(FROM_TZ(TO_TIMESTAMP('22:00','HH24:MI'),'US/Eastern') AT TIME ZONE '+00:00','HH24:MI') AND 
  TO_CHAR(e.begin_time,'DDMMYYYY HH24:MI') >= TO_CHAR(FROM_TZ(TO_TIMESTAMP('Mar-31-2012 00:00','MON-DD-YYYY HH24:MI'),'US/Eastern') AT TIME ZONE '+00:00','DDMMYYYY HH24:MI') AND 
  TO_CHAR(e.begin_time,'DDMMYYYY HH24:MI') <= TO_CHAR(FROM_TZ(TO_TIMESTAMP('Apr-2-2012 23:59','MON-DD-YYYY HH24:MI'),'US/Eastern') AT TIME ZONE '+00:00','DDMMYYYY HH24:MI') 

Thanks in advance,

Dan

Answer 1

The performance of the following might not be what's wanted, but if you cast the DATE value to a TIMESTAMP you can use the EXTRACT function in a manner similar to:

SELECT *
  FROM your_table e
  WHERE e.BEGIN_TIME BETWEEN TO_DATE('31-MAR-2012 00:00:00',
                                     'DD-MON-YYYY HH24:MI:SS')
                         AND TO_DATE('02-APR-2012 23:59:59',
                                     'DD-MON-YYYY HH24:MI:SS') AND
        EXTRACT(HOUR FROM CAST(e.BEGIN_TIME AS TIMESTAMP)) BETWEEN 6 AND 22

Share and enjoy.

Answer 2

When trying to grab data based on a portion of a date field, of course the index will not be used. there just ain't any workaround to that. You could look into adding a function-based index, however, to index on the minutes of the day in EST. Or, perhaps, add a new column to hold minutes_est, have it populated by an insert/update trigger and then base your query on that.

If this is a regularly used query, and the performance of a full table scan isn't cutting it, then yes - I think this is one of those times where you might need to do some redesign based on your needs for this.