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

i wnt 2 known more differences,from u.

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.

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