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Thread: Merging two streams the number of fields in output is doubled

  1. #1

    Default Merging two streams the number of fields in output is doubled

    I need to merge two same structured streams (from the same table but with two different select and group_concat command).

    The output has to be the sum of all lines of one stream to the rows of other one.
    I used FULL OUTER merge.

    I.e. 3 rows from 1st and 1 rows of 2nd. Output result 4 rows.

    Why the output stream make a kind of copy of all fields adding _1 ???

    The output is at the end of 3 rows

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  2. #2


    OK probably I did a mistake using Merge Join instead of Sorted Merge.
    Is that one the problem ?

  3. #3
    Join Date
    Jun 2012


    You can use "Append streams", "Sorted Merge" or no step at all to unite two input streams.
    The subtle differences should be obvious after reading the step documentation.
    So long, and thanks for all the fish.

  4. #4
    Join Date
    Feb 2011


    marabu got it almost perfectly =p but yeah, reading docs would solve the problem.

    Main difference is that Append Streams is mostly cosmetic and useless, while Sorted Merge needs sorted inputs and it's output is sorted.

    FULL OUTER is a merge join... actually, now that I think about it, this part of PDI can really be awesomely confusing for newcomers...
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    Quote Originally Posted by gutlez
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  5. #5
    Join Date
    Mar 2011


    Second use of append streams, or just join them up if the structure and order is identical.

    I see Append as synonymous with a UNION, rather than the merges as more of a join when I use them.

    subtle differences should be obvious after reading the step documentation
    <- this guy's funny although I admit the doco's getting better, it's the subtleties which tend to be unclear.

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