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Modifying queries to run optimized

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    Modifying queries to run optimized

    Hi all,

    This is a sequel to the previous thread on getting a pointer to a form's query and imposing it on a second form. Since I couldn't make that happen I moved to speeding up a new query on the 2nd form.

    In the course of doing this I explored the some parameters of query syntax which effect whether it will run optimized. Since I learned something I thought other's might like to see my results.

    I wouldn't want to overclaim. I started out pretty much at the bottom knowing only that queries including the operators .and. .or. .not. don't optimize.

    But what about variables...?

    Please inform me of any errors and/or omissions you discover.

    There is a readme (wordpad) which opens from a button on the form.

    Bill
    Bill Hanigsberg

    #2
    RE: Modifying queries to run optimized

    That's good, Bill. You've moved up from one of the slowest methods to the second fastest method. Don't quit now.

    Comment


      #3
      RE: Modifying queries to run optimized

      And the fastest method is?
      Bill Hanigsberg

      Comment


        #4
        RE: Modifying queries to run optimized

        Bill

        Attached is a method 4, which I think you will see is a little faster.

        Jerry

        Comment


          #5
          RE: Modifying queries to run optimized

          Jerry,

          Method4 and Method3 are essentially the same, are they not?

          -- tom

          Comment


            #6
            RE: Modifying queries to run optimized

            Hi Tom,

            Four appears a trifle faster. I infer Jerry is telling us that the escape character forces the variables to be evaluated only once (rather than for each record?) although I wouldn't have known this had he not suggested this method. Am I correct, Jerry?

            I have an additional question. So long as I am going to create an additional field to index in order that queries run optimized, I'd like to get maximum mileage from it.

            Hence, if I create this field:
            D30 2001 1 2 38796191 C01 (spaces here for legibility)
            and create two indexes based on substrings as follows,
            D30 2001 1 2
            D30 2001 1
            Will queries on each of the substrings optimize?

            I run lots of queries on various substrings of the long string which uniquely identifies a course-department combination.

            Thanks,
            Bill
            Bill Hanigsberg

            Comment


              #7
              RE: Modifying queries to run optimized

              Tom,

              Yes and no. The expression is the same, but using the quotes (chr(34)) around the value for the variable causes the expression to treat the value of the variable as simple text. The variable value is inserted into the expression, rather that the pointer for the variable. The filter

              "between(Dept_Yr_Sess,"+chr(34)+var->vBegin+chr(34)+","+chr(34)+var->vEnd+chr(34)+")"

              When evaluated, actually becomes

              between(Dept_Yr_Sess,"D3020011","D3020013")

              Each record is evaluated against a fixed value, not a variable that needs evaluated each time.

              This have been discussed by a number of people on the message board in the past. The real gains occur if there are a number of variables or a large number of records. Then this method becomes much faster.

              Jerry

              Comment


                #8
                RE: Modifying queries to run optimized

                Jerry,

                Thanks. As strange as it may seem, I don't recall hearing about this before now. I'm glad to know about it. Would you consider writing it up as a 'tip' for the Alpha Software tips page?

                -- tom

                Comment


                  #9
                  RE: Modifying queries to run optimized

                  Thanks Jerry,

                  I see this now and even remember the discussions. It will make a difference for me as my actual table size exceeds the sample.

                  On my second question, I may have answered it, unhappily in the negative.

                  I created a field populated with the longer string and indexed on the first 8 characters so the key values were the same as for the index based on the other field. I deleted the index on the 8char field and the queries slowed down enough that I got to look at the blue bar.

                  So I appear to need several fields to ensure optimization of queries. Won't kill me but I wish I didn't.

                  Regards,
                  Bill
                  Bill Hanigsberg

                  Comment


                    #10
                    RE: Modifying queries to run optimized

                    There is an article on the Learnalpha site by Dr Wayne titled "Mysteries of Query & Filer Syntax" dated 5/1/99 which covers this method in a slightly different way. I just chose to replace the single quotes with the ascii value for a quotation mark. I just can't keep the single and double quote concepts straight.

                    Jerry

                    Comment


                      #11
                      RE: Modifying queries to run optimized

                      Jerry, I'm very familiar with the article you mention, and will review it again. I don't recall making the connection between the syntax formatting discussions and performance enhancement possibilities. Thanks for clarifying. -- tom

                      Comment


                        #12
                        RE: Modifying queries to run optimized

                        Bill,
                        Ira had some interesting comments on filtered expression:
                        If you do a search on:
                        "Filter expression is not logical"
                        and look for Ira's posting, there is some interesting stuff.
                        John

                        Comment


                          #13
                          RE: Modifying queries to run optimized

                          Thanks for this.

                          Best,
                          Bill
                          Bill Hanigsberg

                          Comment


                            #14
                            RE: Modifying queries to run optimized

                            Faster yet.

                            Comment


                              #15
                              RE: Modifying queries to run optimized

                              I know it's not a secret, so...
                              [b]
                              'Set values here for testing purposes
                              term_s = "20011" 'winter 2001
                              term_e = "20013" 'fall 2001
                              dept = "D30"

                              vBegin = dept-term_s
                              vEnd = dept-term_e

                              f = :form.load("sects_select","Dialog")
                              t = f:tables:Sections.this
                              idx = t.index_get("dys")
                              range.flags = range_index .or. range_first .or. range_last
                              range.index_pointer = idx
                              t.range_add(vbegin,vend)
                              t.fetch_first()
                              f.resynch()
                              fw=f.width
                              A5_Width=ui_info(0)
                              f.left=A5_width-fw 'all the way to the right
                              f.top=0

                              f.show()

                              t.range.drop()
                              f.close()
                              END
                              Peter
                              AlphaBase Solutions, LLC

                              [email protected]
                              https://www.alphabasesolutions.com


                              Comment

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