Hi dear friend,
would you please help to clarify the usage of join stage and lookup stage ?
I have below questions.
1, in join stage, is it necessary to sort both input links ? what will happen if we don't sort but just patition the input data by the keys?
2, sometimes the join stage and lookup stage can do the same time, in what condition should i use join stage, and when should i use lookup?
Thanks!
question about join/lookup
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question about join/lookup
wuruimao
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Join stage needs sorted inputs for efficiency. With sorted inputs it only needs to deal with a single key value at a time. Depending on your settings, if you don't sort your data DataStage will insert a tsort operator so that they are sorted (you can see this in the score).
Lookup can't do right outer join or full outer join. Lookup can't work with a reference data set that won't fit in memory.
Lookup can't do right outer join or full outer join. Lookup can't work with a reference data set that won't fit in memory.
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Any contribution to this forum is my own opinion and does not necessarily reflect any position that IBM may hold.