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Thread: How does olap engine work for SQL queries???

  1. #1
    Join Date
    Jul 2013
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    15

    Default How does olap engine work for SQL queries???

    Dear all,
    I would like to know about olap engine.
    - In CDE, when we create dashboard, we can use both MDX and SQL for datasource. At that time, olap engine parses, validates and executes the MDX queries. But how about SQL queries??? how does olap engine work for SQL queries???

    I would like to know it seriously. Please, someone who knows explains me about that.
    Thanks in advance for your help.

    With regards,
    nnt

  2. #2
    Join Date
    Jan 2013
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    357

    Default

    Here's the big picture: a ROLAP engine like Mondrian parses and evaluates MDX, determining what data is required to return the cellset requested. It will attempt to retrieve that data from cache. If there are cache misses it will fire one or more SQL queries to load what's missing. A client of the ROLAP engine has no need to think about what SQL is required.

  3. #3
    Join Date
    Jul 2013
    Posts
    15

    Default

    Thanks for your reply, mcampbell.

    What I would like to know is if Mondrian parses and evaluates inputted MDX and retrieves data from cache or fire one or more SQL queries to load data,
    how does Mondrian work for inputted SQL???
    According to its architecture, it accepts MDX queries and returns resultset. If we use SQL queries, isn't Mondrian used to get data from cache or Database for SQL queries???
    If so, what are the differences between using MDX queries and using SQL queries???

    Please, someone who knows explains me about that.
    Because I'm researching about how Mondrian work in Pentaho Community Edition and Enterprise Edition. When I read the documentation of Mondrian, it only includes how it works for inputted MDX queries but not for inputted SQL queries.

    Thanks in advance for your help.

    With regards,
    nnt

  4. #4
    Join Date
    Jan 2013
    Posts
    357

    Default

    Mondrian does not take SQL as input. If you're using SQL in CDE it's not being handled by Mondrian.

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