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  • INTERVIEW QUESTIONS DATA WAREHOUSING DATASTAGE DETAILS
    Question :
    What is the exact difference betwwen Join,Merge and Lookup Stage??


    Category DataStage Interview Questions
    Rating (0.4) By 1161 users
    Added on 7/26/2006
    Views 1982
    Rate it!
    Answers:

    The exact difference between Join,Merge and lookup is

    The three stages differ mainly in the memory they use

    DataStage doesn't know how large your data is, so cannot make an informed choice whether to combine data using a join stage or a lookup stage. Here's how to decide which to use:

    if the reference datasets are big enough to cause trouble, use a join. A join does a high-speed sort on the driving and reference datasets. This can involve I/O if the data is big enough, but the I/O is all highly optimized and sequential. Once the sort is over the join processing is very fast and never involves paging or other I/O

    Unlike Join stages and Lookup stages, the Merge stage allows you to specify several reject links as many as input links.



    The three stages differs with each other with respect to
    1>Input Requirements
    2>Treatment of unmatched records
    3>Memory Usage

    Join requires less memory usage
    Lookup requires more memory usage and
    Merge requires less memory usage

    To know more differences, you can mail me. There are almost 12 differences that i can explain you



    Posted by: Vishwanath    

    Contact Vishwanath Contact Vishwanath

    i wnt 2 known more differences,from u.



    Posted by: rasool    

    Contact rasool Contact rasool

    The main difference between the Join,Lookup,Merge is
    1)In the Join stage we can perform 4 Joins i.e Inner join,Left outer Join,Right Outer Join,Full Join.
    2)Join doesn't have Updated link,Reject links.we can't capture unsatisfied condition data.

    1)In the Lookup stage it has only two joins i.e drop(inner),continue(left outer join).
    2)In this we have to mention common column.
    3)Unsatisfied data will come from source only.

    1)The main difference of Merge is
    It has only two Joins i.e drop(inner),keep(loj)
    2)It will work on common key column
    3)The Unsatisfied data will come from Updated link(reference) to Reject link.



    Posted by: pradeep    

    Contact pradeep Contact pradeep

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