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An .OR. between betweens

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    #1

    An .OR. between betweens

    I aam wondering if lightning query optimization ca happen in a form query if I have a filter that looks like the following:

    between(orderstatus,"1","3") .OR. between(orderstatus,"5","7")

    Some people say that optimization can happen with AND/OR/NOT links and some people say otherwise.
    Tags: None
    #2
    RE: An .OR. between betweens

    This is from the book.
    The condition expression must use operators that are compatible with Lightning Query Optimization. These include:
    ? Equals (=)
    ? Exactly equals (==)
    ? Greater than or equal to (>=)
    ? Greater than (>)
    ? Less than or equal to ()
    ? BETWEEN(..)
    ? SMATCH - see note below
    ? Wildcards (* and ?) - see note below
    ? .NOT.
    ? .AND.
    ? .OR.
    NOTE The SMATCH function and the wildcards * and ? can only be used with LQO if they appear at the end of the expression. For example, a search for McC* can be optimized since the wildcard operator appears at the end, while a search for *stein cannot be optimized, since the wildcard operator begins at the beginning.
    Partial Compatibility
    In some cases, only part of your query's selection expression can be used with Lightning Query Optimization. In this case, Alpha Five applies the optimization algorithm to the compatible part, and uses Alpha Five's standard query algorithm to evaluate the rest.
    For example, suppose you have a table of customers for which you have created an index that sorts records by the field City. You then create a query which uses the following selection expression:
    (CITY = "BOSTON").AND.("Commonwealth" $ ADDRESS1)
    Because the second half of the expression uses an operator that is not compatible with LQO and a field which is not used in a pre-existing index (ADDRESS1), Alpha Five applies Lightning Query Optimization to only the first part of the expression.
    Furthermore, in cases where the selection expression evaluates to TRUE for most of the records in the table or set, Alpha Five may analyze the query and determine that Alpha Five's standard query algorithm is more suitable. In this case Lightning Query Optimization is not used.

    Comment

      #3
      RE: An .OR. between betweens

      Greg,

      I have not done extensive testing of version 4.5 or version 5, but I can tell you that version 4 did not seem particularly clever in it's ability to use LQO.

      I'm guessing, but I believe that the .OR. operator would not be used. As far as I can tell, A5 V4 looked for a portion of an equation that would allow it to effectively set a begin and end of a range of an index that would minimize the number of records that it needed to look at. In your case, it had 2 sections of the index that it would need to get, and I don't believe it was smart enough to do it.

      This is an area that I'm sure has constant tinkering by Alpha Software, and thus may change significantly from version to version and even maintenance release to maintenance release. The guideline I use is to present the equation (by building an equation in a character string -assuming it is dynamic) that is already simplified. For example, for your case(and assuming only integer numbers are valid), I would get the minimum and maximum values (1 and 7) and present the equation as such

      between(orderstatus,"1","7").AND..NOT.(between(orderstatus,"4","4"))

      Alternatively,

      between(orderstatus,"1","7").AND..NOT.(orderstatus=="4")

      The way I can tell for sure is that I actually run queries and test for the length of time that it takes to process (using NOW() function). Note that NOW() has a resolution of about 1/18th of a second, thus it is possible for the difference results to be off by as much as .12 seconds. This means that if your entire length of query is dealing with a small number, it is hard to tell if the numbers are faster or slower. Finally, you must force the query to always evaluate (or delete the query results). If not, A5 sees that it was previously run, and doesn't even run it the 2nd time.

      Regards,

      Ira J. Perlow
      Computer Systems Design & Associates
      [email protected]
      Regards,

      Ira J. Perlow
      Computer Systems Design


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      Comment

        #4
        RE: An .OR. between betweens

        Thanks Ira I have reconfigured my queries to reflect your suggestions it will be interesting to see how things turn out as the database grows. I am a little lost on what you mean by reevaluating the query. The user in my case presses a button to access the form and the query is invoked I had thought that when the form is closed the query is closed. If this is not the case how do you go about reevaluating the query?

        Comment

          #5
          RE: An .OR. between betweens

          Thanks for pointing this out. I just don't understand why Dr. Peter Wayne indicated in his book "Xbasic for Everybody" in chapter 20 Queries section that "for optimization to take place, the query filter can only reference one table, and the query expression cannot use the conjunctions .and., ,or., or .not..

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