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Index on date/time field - useful?

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    Index on date/time field - useful?

    This is possible, but is it useful? I may be missing a technique for using a date/time value in queries?

    After creating an index on Update_Time field, doing a find by key for a value like "06/26/2014 11:11:25 13 am", which does exist in the data, goes to the first record in the file. Of course the search value was a character string vs. the index being a time(?) value. Find by key for ctodt("06/26/2014 11:11:25 13 am") goes to the last record in the file, so no better.

    I used query genie to create the following
    between(update_time,ctodt("06/25/2014 9:00:00 00 am"),ctodt("06/26/2014 11:59:00 00 am"))

    This returns ALL records on 06/25/2014, not just the ones in the morning. It also does a full scan of the table, taking 35 sec. In contrast, doing a between() query on a character field takes < 1 sec. The table has 300K records.


    Next step is to create a character index for Update_time like the following, using a 24 hour clock.
    TIME("yyyy/MM/dd 0h:0m:0s.2",UPDATE_TIME)

    Then find by key does find the correct record instantly. But a query for a range of records still does a full scan of the table, requiring 30+ seconds.
    t=table.open("person")
    i = t.query_create("","between(time(\"yyyy/MM/dd 0h:0m:0s.2\",update_time),\"2014/06/24 09:00:00.00\",\"2014/06/24 13:59:00.00\")","")


    Anyone had better luck getting quick response from a query on a time field?

    Bill.

    #2
    Re: Index on date/time field - useful?

    Seems like I helped someone with searching/indexing a time field and we wound up with the index definition as ctime(timefield). Don't think the delay was noticeable, but it has been a while.

    The query was using ctime(sometimevalue).
    There can be only one.

    Comment


      #3
      Re: Index on date/time field - useful?

      Originally posted by Stan Mathews View Post
      Seems like I helped someone with searching/indexing a time field and we wound up with the index definition as ctime(timefield). Don't think the delay was noticeable, but it has been a while.

      The query was using ctime(sometimevalue).
      Thanks Stan,

      That works also, but after building the index, query still does full scan of table for 30 seconds.
      i = t.query_create("","between(ctime(update_time),\"20140624090000000\",\"20140624135900000\")","")


      Bill.

      Comment


        #4
        Re: Index on date/time field - useful?

        Hi Bill:
        Did you get this figured out? How did you define the time index? As just "time" or as Ctime(time)? I think you would need CTIME(TIME) for LQO to work.

        In the days before Y and T field types I used a calculated field in the main scheduler table and C fields formatted for LQO to achieve instant record retrieval regardless of the size of the table. In any event, the key was a combination of date, C time fields and calculated field(s) that were indexed.

        The calc fields were defined as

        Code:
        CDATE(dte)+PADL(LTRIM(STR(TOSECONDS(t1))),6,"0")
        where "dte" was a date field for the appointment date, and t1 a "C" value for the appointment time.

        In use, the process was pretty simple. Here's some sample query code to retrieve the appointments between times on a given date.

        Code:
        dim dte as d = {01/01/2013}
        dim t1 as c = "09:00 am"
        dim t2 as c = "11:00 am" 
        dim look1 as c = CDATE(dte)+PADL(LTRIM(STR(TOSECONDS(t1))),6,"0")
        dim look2 as c = CDATE(dte)+PADL(LTRIM(STR(TOSECONDS(t2))),6,"0")
        qfilter = "BETWEEN(QUERY,\"" + look1 + "\",\"" + look2 + "\")"
        qorder = "Link1"
        t = table.open("appointment_schedule")
        dim tidx as p = t.order(qorder,qfilter)
        ?tidx.records_get()
        = 13
        t.close()
        Both Query and Link1 were table calculated fields with the same definition and both were indexed. I can't remember why this redundancy existed.

        Anyway, regardless of table size, a query for appointments was always instant. For a full day it would return anywhere from 40 to 60 records (and sometimes more) in a flash.
        Finian

        Comment


          #5
          Re: Index on date/time field - useful?

          Hi Finian,

          Well, I have not gotten the speed down. It seems that a straight index on a time field has no use, or I could not find a way to use it.

          I did test 2 different character indexes on the time field with results below. The indexes for the update_time field were
          time("yyyy/MM/dd 0h:0m:0s.2",update_time) and
          ctime(update_time)

          First set of queries on time field shows that query on time field is the same if there is an index or not. Second set of queries on a character field was 10x faster, but I still got the same speed if there was an index or not. Of course for the second set I was just making something up to have similar processing for index key.

          Table 270,000 records.
          t=table.open("person")
          ------------------------
          i = t.query_create("","between(time(\"yyyy/MM/dd 0h:0m:0s.2\",update_time),\"2014/06/24 09:00:00.00\",\"2014/06/24 13:59:00.00\")","")
          took ~ 35 sec to build index and 35 sec to run query. if no index, query still 35 sec.

          i = t.query_create("","between(ctime(update_time),\"20140624090000000\",\"20140624135900000\")","")
          took ~ 35 sec to build index and 35 sec to run query. if no index, query still 35 sec.

          ------------------------

          i = t.query_create("","between(left(person_id,3)+\".\"+right(person_id,3),\"150.000\",\"650.000\")","")
          took ~ 3 sec to build index and 3 sec to run query. if no index, query still 3 sec.

          i = t.query_create("","between(substr(address1,2,5),\"23\",\"45\")","")
          no index built, query took 3 sec.

          ------------------------

          Bill.

          Comment


            #6
            Re: Index on date/time field - useful?

            Could having indexed, calculated fields in the table (which match the query filter strings exactly) speed the query? That was my situation. The largest scheduler table that I recall had about 125,000 records and even then the returns were instant. Still 3 seconds is not too bad.
            Finian

            Comment


              #7
              Re: Index on date/time field - useful?

              Bingo! That's what is great about this board. When you can't see something, others can. Query is now instant since the index order expression is simplified with the calc field.

              Thanks Finian.

              Bill.

              Comment


                #8
                Re: Index on date/time field - useful?

                Great, glad to help.
                Finian

                Comment

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